If the four major automotive processes were compared to the legendary martial arts masters, the coating process would undoubtedly hold a paramount position. It may not appear as flashy as the others, but without it, the whole operation simply cannot function.
Automotive coating generally refers to the coating of various types of vehicle bodies and components, including passenger cars, buses, and trucks. Simply put, automotive coating is a combination of fashion and technology, making vehicles stylish while reliably serving their purpose at all times.
Purpose of Coating:
1. Protective Function
Fundamentally, 90 percent of automobile manufacturing uses steel. If cars were not painted, the consequences are obvious. The vehicle's service life would be greatly reduced, and various types of corrosion would inevitably occur. This demonstrates the necessity of automotive painting. It is actually similar to applying a screen protector on a phone, if you do not understand what that means, well, you can just go without one.
2. Enhanced Aesthetics
Yes, that is right, it is about enhancing the visual appeal. When your coating stands at the forefront of trends, and the paint you use has a premium feel, without exception, it elevates the owner's aesthetic sophistication. Of course, there are also cases where the attempt falls short, resulting in a less than desirable outcome.
Automotive Paints
Automotive paints mainly refer to the paints and auxiliary materials used for coating and repairing sedans, trucks, buses, and other modified vehicles. We can think of them as cosmetics for vehicles, where different products are used for different areas, and key parts require essential protection.
Automotive paints can generally be classified by their usage location on the vehicle and the function of the coating:
(1) Surface treatment materials: mainly including cleaning agents and phosphating agents; (for treatment purposes)
(2) Automotive primer; (undergarments)
(3) Automotive mid-coat; (innerwear)
(4) Automotive topcoat; (outerwear)
(5) Auxiliary materials: including solvents, curing agents, putty, polishing wax, etc. (accessories)
When mapped out this way, cars and people are not so different!
Coating Process
Since the body-in-white is like a newborn baby that has not yet adapted to this world, we must provide special care for its delicate skin. Similarly, due to the importance of coating for a vehicle, the coating process is highly complex. The coating process is mainly divided into two parts: surface treatment (similar to the wiping process before applying a screen protector) and the coating application process. However, as principles dictate, we cannot simply apply paint however we want. Therefore, before coating, we must first understand the coating process system, so that we can follow the system and avoid the mistake of rushing ahead blindly.
Common coating process systems, classified by number of coating layers, can be divided into two-coat systems (primer plus topcoat); three-coat systems (primer plus mid-coat plus topcoat or metallic basecoat/clearcoat); and four-coat systems (primer plus mid-coat plus topcoat plus clearcoat, suitable for luxury vehicles with higher coating requirements). Indeed, the more layers applied, the more premium the result!
The most common is the three-coat system. Passenger car bodies, buses and touring coaches, and truck cabs with high decorative requirements generally adopt the three-coat system.
Classified by drying conditions, coating systems can be divided into baking systems and air-dry systems. Baking systems are suitable for mass-produced assembly line automotive coating; air-dry systems are suitable for small-batch production automotive coating and large special vehicle body coating. This is quite straightforward to understand, baking them together is the baking process, but some vehicles prefer to be different, and with an inclusive mindset, we let them dry on their own.
The general coating process is as follows:
Now that we have a guiding framework, we can begin the coating process!
1. Pre-painting Surface Treatment Process
This can be thought of as laying the foundation, similar to basic training in sports, refining the body-in-white to a state where it can be further sculpted. This involves removing oil, dust, and rust from the workpiece surface, as well as removing old paint layers during repair work, to improve the surface condition of the workpiece. It also includes mechanical processing and chemical treatment of the workpiece surface based on specific circumstances, such as phosphating, oxidation, and passivation treatment.
2. Coating Application
(1) Primer Application
The primer coat is the foundation of the entire coating system and can be considered a critical step. The adhesion between the automotive coating and the metal, as well as the corrosion protection, mainly rely on it. The primary method used is air spray painting (high-pressure airless spraying can also be used) to apply the primer. This is the process of putting on undergarments, except these undergarments are sprayed on. Only when the primer is applied well does the vehicle have a solid foundation.
(2) Putty Application
Applying putty is essentially a leveling process, removing wrinkles and imperfections.
(3) Mid-coat Application
Using electrostatic spraying or air spray methods to apply the mid-coat can improve the chip resistance of the coating and enhance adhesion to the primer. As the middle layer, it dutifully serves as a bridge, helping the primer below fill imperfections, and then humbly prepares to receive the topcoat.
3. Topcoat Application
Using electrostatic spraying or air spray methods, this is the process of dressing the vehicle. Whether it looks good after dressing depends not only on the craftsmanship but also on the designer.
At this point, the coating of a vehicle is essentially complete. To make further transformative changes, one can only rely on cosmetic refinement techniques. What nature has given you is what you have, keep striving!
Excerpted from "Modern Paint and Finishing"
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