Underbody Coating

UNDERBODY COATING:

Underbody coatings are the protective coatings used to protect the vehicle chassis from external environment to ensure the integrity and safety of cars.The use of underbodycoating plays a very important role in the service life of of the vehicle.In general it is required to spray such a protective coating in the manufacturing of the new car.Due to high competitivenss of new car sales,car producers have pressure to reduce the manufacturing cost.So that they reduce or even completely eliminate the use of underbody coating where it is not to be easily seem by car owner.

It also protects the parts like internal body panel,frame rails and other inner cavities that are not physically accessible but are prone to corresion.The underbody coating provides longterm protection from corresion to car’s underbody.The underbody coating also helps in reducing the NVH(Noise and Vibration Harshness)level of cars.The underbody coating also increases the life span of the car.

Uses of underbody coating:

Protect against rust and corrosion:

The primary objective of getting underbody coating is to prevent the metal components that are exposed on the bottom side of the car which damage from corresion.The adverse effect of the corresion can be overcome by applying a rubberised anti-rust coating all over the belly of the car.

Prevents from stone chip:

There are thousands pieces of stones on the road and they are constantly hitting your car on the underbody,wheel arches,sills and the trunk lower part while driving on road.In some cases the underbody might be scratched by uneven roads.As such the thin corrosion protection coating on the metal sheet will be distroyed and leave the bare metal exposed to the air,which will soon comes to corrosion when contact with the moisture in the air.If not promptly getting anti-rust treatment the the rust will soon spread to large area.Underbody coating or anti-stone-chip coating is a thick elastic layer which could not be easily damaged by stone chipping or scratch therefore could be basically protect the metal sheet of the under body.

External influence:

External environment such as baking from the hot road in summer ,the road’s&nbpa;anti-frozen gent in winter,raining water and the salty water in the atmosphere,will attach the under body of a car areas,the wind from the sea will bring more salt to air,which will accelerate the corrossion and reduce the service life of a car.While the under body is convered by a thick and tight layers ,it would act as a strong barrio to prevent these external substances attaching the metal sheet.

Keep the value :

A car could keep a high value while it is well maintained.It means that it a car is well treated on under body protection it could keep the car in a good condition and extend the car’s service life or could charge a higher price in a used car trading.

Improve driving comfort:

After curing, the under body coating becomes a thick elastic coating covering the whole under body ,which could act as a good dampenong material,significantly reduce the vibration of the metal sheet and reduce the noise inside the car.

Prevents Paint chippings

Running on the highway or while pacing through a city road,you will often encounter sharp gravel or any other unattended object hitting the belly of your car with high momentum.This scrapes and chips off the metal from down below.A thick layer of under body coating definitely comes to aid and minimises the effects of such contacts on the body

Minimize sound:

It minimizes the sound from the underneath the car resulting a noiseless,smooth driving experience.

Heat insulation:

It insulates the interior of the car from extreme temperatures from beneaths the vehicle providing a comfortable cabin experience.

Types of underbody coating:

Rubberized underbody coating:

• Rubberized underbody coating is easy to apply and offers sound-cushioning as well as protection from dust,moisture and dings or dents.
• In addition to the underbody coating rubberized is also safe to use on the wheels well and quarter panels and dries to a soft rubbery finish that prevents further rust,damage or moisture seeps
• The coating can be painted over and if necessary for bodywork can be easily removed with an underbody coating spray
• Overall Rubberized is generally the best option for protecting your vehicle undercarriage as it provides the simplest and best protective measures against rust and moisture.

Polyurethane undercoating

• The other option for undercoating your vehicle is to use a polyurethane based sealant.This type of vehicle undercoating is a little bit quicker and esaier to apply.
• Oftentimes polyurethane coating will come in canister preload into an applocation gun.
• This type of sealent works by seeping into all cracks and seams, displacing salta,moisture and oozing around the rusty areas to bond with and to protect unoxidized metal.It also sands quickly in case you’ll need to perform bodywork and can be painted over.
• On the otherside this type of car undecoating generally requires a little bit more surface prepration work before applying -sanding and applying an etching primer to bare matals before using are generally recommended.

Wax or paraffin based coating

• A paraffin based underbody coating will be the cheapest and quickest option available with which to protect the undercarriage of the vehicle.
• However it will wear off quickly than other type of undercoating and will nead to be stripped and reapplied at least once a year.
• Wax based undercoating never truly harden.During the application they drip or flow into seams and cracks to provide protective properties.

Asphalt-Based undercoating:

• For standard vehicles any of the mentioned types of undercoating will provide sufficient protection .
• For large trucks and heavy machineries,asphalt based undercoating provides a bit of extra durability against rocks,chips and moisture.
• Asphalt -based undercoating generally contains a little bit of rubberized material that setup firmly and helps soften the noise.

Procedure of underbody coating:

Underbody coating consists of the following steps:

• Pre treatment
• Electrodeposition
• Rustproof material
• Primer
• Topcoat

Pretreatment:

The first sequence in preparing the BIW for subsequent coating is pretreatment sees . Preatrament removes & clean excess metal & forms an appropriate surface structure enabling bonding of a corrosion protection layer. It consists of cleaning the body surface to remove remaining oils from the staming process & welding residues through three primary liquid dip processes of degreasing, conditioning, & phosphating. Pretreament helps the primer to bond onto the metal. A phosphate treatment applies an inert layer of metal phosphate, providing resistance to corrosion spread. The degreasing solution is composed of alkaline salts & surfactants & can include caustic soda, sodium carbonate. The surfactants are types of detergents for emulsifying oils & lubricants on the BIW. In surface conditioner which creates nucleation sites for phosphate crystal growth. It increases the number of crystallization nuclei on the metal surface that enchance bonding mechanism for the subsequent phosphate sequence. Finally, the liquid dip phosphate ions, nitrate ions, zinc & hydrogen ions. The free acid etches the steel surface, causing hydrogen to be released while metal phosphate ions are precipitated onto the surface in a crystalline form.

Electrodeposition:

E-coating involves dipping automobile bodies into the coating solution and passing an electric current through the body & the liquid ED paint solution. Because of the chargednature of this coating process, the ED paint penetrates into places a spray would not reach.

During operation, a mixture of resin, binder, and a paste containing the pigments is fed into the ED tank. The automobile body is lowered into the tank, and an electric current applied; the solution in the tank consists of 80-90% deionised water and 10-20% paint solids.The resin is the backbone of the final paint film and provides corrosion protection, durability, and toughness. Pigments are used to provide color and gloss. After E-coat, the automobile body enters a bake oven, in which heating and keeping at a temperature of 160C for 10 min causes film curing to promote maximum performance properties. The oven temperature and heating time primarily enchance chip resistance and film adhesion to the body; corrosion protected is affected less by these conditions. Because surface roughness influences the smoothness and brilliance of the topcoat, some sanding of the surface is usually performed to remove or eliminate defects before the body enters the next application step. A common challenge in the current E-coating process is that of water spots that contaminate coated surfaces. If water spots are present, they have removed by sanding. Hence, it is necessary to use well-deionoised water and routinely monitor its conductivity. Alternatively, operators also add surfactants or ultrafiltrates to the water rinse zone to eliminate or manage water spots.

Rust proof material:

The third step is underbody coating and seam sealing using PVC and displays the lower door sections and rocker panel locations where PVC or urethanes are applied as an anti-chipping protection, and shows the cross section of this layer with respect to the other coatings on the body parts. During this third step, it is also typical to apply a soft tip primer coat that improves the chipping resistance . This layer is applied to the front edge of the hood , which is an area prone to chipping shock, using a high elastic resin that resides between the ED and primer coats. Also, during the third step, the radiator supports, wheel housing, and under rear areas of the body are coated with a relatively dull black pigment called a blackout coating.

Primer:

The fourth coating step is the primer. It can be water-borne, solvent-borne, or a powder. The primer fills and smoothes minor imperfections and scratches that may be created during prior steps and by the intermediate sanding or grinding used to remove small imperfections. It also provides additional protection against corrosion and maximizes adhesion between it and the E-coat and basecoat; thereby, the primer incrases paint durability. Primer coating operations in an automobile assembly plant are usually implemented in three stages: Interior coating, Exterior coating, and then cutting in an oven. Manual spray painting is used for the interior coating of the doors, engine compartment, and luggage or trunk space. Some of the areas are not sprayed with basecoat. It is important that are primer color matches the basecoat to be able to impart uniform coating appearances between interior and exterior coats.

Topcoat:

The final step in the body coating process is to apply the topcoat, which consists of two layers the basecoat and clearcoat. Basecoat: It contains the primary coloring pigments. As part of the topcoat, the basecoat is third layr added to the car after the primer and before the clearcoat. It imparts the automobiles color; roughly 40,000 base coat color are known today , and approximately 1000 new colors are added to this list each year. Three different types of basecoats are used for automobiles, including solvent-borne medium solids (MS), solvent-borne high solids (HS), and water-borne. Clearcoat: The final coating on an automobile surface is the clearcoa; it provides durability, environmental etch, and scratch resistance to the overall coating. It protects against damage such as fading that is caused by UV rays from the sun and imparts a gloss and depth that otherwise are not as vivid. The clearcoat also makes repairs and maintenance easier. Environmental etch is an appearance issue associated with the formation of permanent water spots or nonremovable marks from bird droppings, tree resin, or other chemicals after contact with an automobiles surface. The physical damage resulting from etchi=ng is associated with a localized loss of material and deformation or pitting of the clarcoat surface.

Pros:

• It provides a extra layer of protection against rust and corrosion
• It will extend the life of vehicle
• It can be applied to damaged areas
• It can be self applied
• It minimize the sound from underneath the car
• The coating doesnot chip away when hit by stones.
• It insulates the interior of the car from the extreme temperature from beneath the vehicle.

Cons:

• It won’t do anything about the corrosion which is already present
• It adds weight to the vehicle
• It works best on new cars
• An under coating is not impervious to damage.
• It must be reapplied every 3 to 5years for best reasult.
• The underbody coating is expensive