Underbody Coating

Challenge No 2 : Preparing a detailed report on under-body coating mechanism.

Under-Body Coating :

In Indian road conditions, a cars underbody is most prone to corrosion. Underbody coating provides long term protection from corrosion to car’s underbody. It also protects parts like internal body panels, frame rails and other inner cavities that are not physically accessible but are prone to corrosion.

Modern Under-Body Coating :

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

Fig : Summary of coating tasks for specific areas.

Fig : Automotive coating layers, their thicknesses and purposes for an exterior surface.

Steps Involved in Modern Under-Body Coating :

1) Pretreatment :

2) Electrodeposition (ED) :

1) 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 materials) are primed before applying additional coatings.

2) E-coating involves dipping automobile bodies into the coating solution and passing an electric current through the body and the liquid ED paint solution.

3) Because of the charged nature of this coating process, the ED paint penetrates into places a spray would not reach. The ED paint is promoted to bond with the metal substrate, and a uniform coating thickness is produced. The result is an insoluble, deposited layer with a very high solids content and firm adherence to the pretreated body

Fig : Electrocoating process.

3) Rust-Proof Materials : Sealer/PVC

1) The third step is underbody coating and seam sealing using PVC (Polyvinyl Chloride) and urethane. This sealing has multiple purposes

2) The sealant is applied around and inside the doors, hood, trunk, and front dash, and onto the exterior and interior of metal joints and outer area of the back wheel well

3) Application of the sealant is accomplished either manually or with robots and prevents air and water ingress and inhibits rust formation

4)PVC and acryl/urethane sealants have also been used in the underbody areas, a process called the Dampening Coat (DC), to impart noise-proofing and vibration-deadening

5) The noise and vibration are transferred from the engine, drive train, suspension system, road noise of the tires, and flowing air, and the underbody sealants reduce noise transfer into the passenger compartment of the automobile

6) During this third step, it is also typical to apply a soft tip primer coat that improves the chipping resistance (resistance against chipping by flying stones or debris).

7) 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.

Fig : The anti-chipping material coating on lower doors and rocker panels

4) Primer :

1) The fourth coating step is the application of a primer surfacer or simply primer. It can be water-borne, solvent-borne, or a powder.

2) It is used to improve adhesion between the E-coat and topcoat, provide chipping protection, enhance paint appearance and, also, be environmentally compatible with emission regulations.

3) The primer fills and smooths minor imperfections and scratches that may be created during prior steps and by the intermediate sanding or grinding used to remove small imperfections.

4) Additionally, most automobile bodies have surface imperfections that arise from the pressing, stamping, and welding operations, and these defects are typically accentuated during the ED step. Hence, although the main purpose of the primer has been to act as a leveler that produces a smoother finished surface

5) It also provides additional protection against corrosion and maximizes adhesion between it and the E-coat and basecoat; thereby, the primer increases paint durability

6) The primer layer is important for stone chip resistance. When chipping exposes the bare metal, the perforation will inevitably lead to corrosion. At the same time, good adhesion of the top coat to the primer surfacer is required to ensure minimal detraction from the visual appearance if chipping has occurred.

7) Hence, it is common to incorporate suitable colors in primers that are compatible with the topcoat, masking damage to the topcoat caused by stone chipping.

Fig : Priming underbody

5) Topcoat :

1) The final step in the body coating process is to apply the topcoat, which consists of two layers—the basecoat and clearcoat.

2) The basecoat contains the primary coloring pigment, and the clearcoat provides a protective coating against environmental effects, corrosion, and UV light degradation, promotes unmatched color retention, and provides a smooth, unblemished, and even finish

3) The body is first coated with either a water-borne or solvent-borne basecoat. If the manufacturer is using a wet-on-wet process, then the clearcoat is applied onto the basecoat after a short flash-off, before curing in an oven.

4) In the absence of a wet-on-wet process, the basecoat is cured before the clearcoat is applied. Independent of which process is employed, typical thermal cure times and temperatures are 30 to 40 min at 125 °C, respectively

Different types of under-body coating :

Underbody coatings are categorised into various types based on the type of material used and also the cost of the material.

1) Wax or Paraffin-based Undercoating :

1) It is the preferred undercarriage coating for cars often driven on highway and normal roads

2) Sometimes referred to as wax-based undercoating, it provides sufficient guard for cars in fairly moist regions

Example : Fluid Film 1, a rust inhibitor, anti-corrosion, and anti-rust undercoat.

Advantages :

1) Readily flows into seams to guarantee any exposed and prone surfaces are protected

2) The most inexpensive undercoating option

3) Conveniently available in spray guy canisters or aerosol cans

Disadvantages :

1) Wears off quicker in comparison to other types

2) Unlike the rubberized type, it does not really dry

3) Needs to be stripped and reapplied at least once a year as soon as signs of wear and tear start to show

Fig : Wax Under-Body Coating

Fig : Wax coating box

2) Rubberized Undercoating :

1) Ideal for cars driven in rough terrain, as its name suggests, this undercarriage coating involves applying a rubber agent to the underbelly to protect and cushion it against dents, dust, and moisture.

2) It can also be applied around wheel wells and quater panel, Considered the best option for standard vehicles when it comes to the different types of undercoating.

Example : rubberized undercoating include 3M 3584 Professional Grade Rubberized Undercoating Rust-Oleum Black Rubberized Undercoating, 3M Body Schutz Rubberized Coating Black, SEM 40523 Low Voc Rubberised Undercoating Aerosol.

Advantages :

1) Easy to apply

2) Quickly applied with no fuss

3) Undercoat can be painted for a neat finish

4) Provides satisfactory protection

5) The simplest way to undercoat your car

6) Safe to apply

7) Truly dries to a soft rubbery finish that prevents further rust, damage, or moisture seepage

Disadvantage :

1) Rubberized undercoatings do a great job of keeping existing rust all covered up and looking sharp, but it does absolutely nothing to slow down the spread of rust and corrosion

2) Sometimes the trapped air and moisture may even contribute to rust formation

Fig : Rubberized underbody coating

Fig : Ruberized coating box

3) Polyurethane Undercoating :

1) Uses a polyurethane-based sealant that comes in canisters ready to be loaded into a spray gun and sprayed to guard the undercarriage of your vehicle.

2) The polyurethane used in this product is a high-quality and durable material that is perfect for any weather condition. It is ideal for standard vehicles.

Example : Polyutherane undercoat is Adam’s SiO2 Infused Invisible Undercarriage Dressing Spray for car detailing.

Advantages :

1) It has a long lifespan and is resistant to wear and tear

2) Easily and quickly applicable

3) Trickles into cracks and rusty spots already present on the underbelly of your car and fills them, hence protecting the

underlying metal

4) Quick and simple to remove, as it sands easily

5) Dislodges salt, moisture, and oozing around rusty areas to bond with and protect unoxidised metal

6) Can be painted over

Disadvantages :

1) For better adherence, needs undercarriage preparation before application

2) Requires time-consuming etching with primer to bare metals

Fig : Polyurethane Undercoating

Fig : Polyurethane Undercoating Box

4) Asphalt-Based Undercoating :

1) Unlike the rubberized, wax/paraffin-based, and Polyutherane undercoatings, this type is made of asphalt and generally also contains some rubberized material that sets up firmly and helps soften noise from the engine.

2)It reportedly has the most damage-resistant properties. Although asphalt-based undercoating is ideal for trucks, military, and all-terrain vehicles, it will also help protect your car, truck, motorcycle, and heavy machinery from the elements.

3)It last long and is best for endurance vehicles that have to undergo heavy road use.

Example : Examples of asphalt-based undercoats are Rust Bullet, an automotive inhibitor paint for rust preventive and protective coating. As well as Skyco-Ospho protective coating.

Advantages :

1) Formulated to protect from dirt, rust, and corrosion, it normally has a shelf life of up to two years. Sold in five-gallon containers

2) Provides extra durability as it is the strongest and thickest undercoating available

Disadvantages:

1) It takes time to harden and so requires more cure time than the other three types

2) Unlike the other three, it is also, not paintable as such, not very aesthetically suitable for standard vehicles

3) For best used only for the undercarriages of utility vehicles and trucks

4) The only type of undercoating with a limited warranty

Fig : Asphalt undercoating

Fig : Asphalt undercoating box

5) Water-based Undercoating :

1) Water-based undercoating is a protective layer that helps your car stay protected from harsh weather conditions. It is made from an advanced polymer that is non-toxic and environmentally friendly.

2) The product can be applied to any surface, including metal, plastic, rubber, and glass. It will keep your car protected from rust, salt, and moisture.

3) This undercoating provides a protective barrier that lasts for only a year-depending on where you drive your car.

4) When it comes to DIY (Do it Yourself) undercoating, this type is the most popular. Coming in an aerosol can, it can be purchased from most automotive shops. This product is easy to apply and can be done in a single day.