FAQ

The application of powder coatings in automotive wheels is becoming increasingly widespread. With stricter national controls on VOCs, new paint coating lines are not being approved, and water-based paint processes still face numerous challenges. Therefore, “Rim Powder Coating” is becoming a consensus in coating applications across more industries. It’s not difficult to see that many wheel manufacturers are also shifting from paint to powder coatings.

1. Advantages of Powder Coatings over Traditional Wheel Coating Types

1.1 Replacing Traditional Primers

Traditional automotive wheel coating processes often employ a four-coat process, which is complex and involves multiple VOC-containing coatings. With the development of powder coating technology, the traditional four-coat process has been changed to a three-coat process, eliminating the original base coat and using a combined primer and topcoat powder, which has become a new development direction in the wheel coating field. The combined primer and topcoat powder integrates the functions of primer and topcoat, significantly simplifying the coating process while ensuring basic properties such as coating adhesion and corrosion resistance. From an environmental perspective, powder coatings inherently possess zero VOC emissions. Adopting this process can reduce VOC emissions in the entire wheel coating process by approximately 20%, effectively reducing environmental pollution. Simultaneously, the reduction in processes significantly increases coating efficiency. A coating process that previously required multiple steps can now be completed in fewer steps, shortening the production cycle and reducing the defect rate caused by improper coordination of multiple processes, further improving the company’s production efficiency.

1.2. Replacement for Metallic Paint

In metallic paint coating of wheels, traditional processes often employ a three-coat process, with metallic paint being a crucial component. However, metallic paints typically contain large amounts of solvents, which release significant amounts of VOCs during coating and curing, making them one of the main sources of VOC emissions in wheel coating. The emergence of metallic rim powder coating provides an effective solution to this problem. The coating process for some metallic wheels has been reduced from the traditional three-coat to a two-coat process, with metallic powder coating directly replacing metallic paint. Since metallic powder coatings are zero-VOC products, VOC emissions during the coating process can be reduced by nearly 50% after switching to this technology, resulting in a significant environmental benefit. In addition to its environmental advantages, metallic powder coatings also exhibit excellent performance. In certain special metallic coating applications, due to the differences in manufacturing processes between powder coatings and traditional liquid paints, the dispersion of metallic powder particles and their bonding with the substrate are more optimized. This allows metallic rim powder coatings to exhibit better interlayer adhesion and compatibility than water-based metallic paints. This means that in multi-layer coating processes, the metallic powder coating can bond better with other coatings, reducing the likelihood of interlayer peeling and cracking, further ensuring the overall quality and lifespan of the wheel coating. Furthermore, with the rapid development of powder technology, more and more environmentally friendly special metallic effects are being achieved. For example, the emergence of chrome-imitation powder coatings can accurately reproduce the metallic texture and luster of chrome plating and can be directly used for automotive wheel coatings, replacing traditional, environmentally unfriendly polishing processes. Traditional polishing processes are not only energy-intensive but also prone to dust pollution. In contrast, chrome-plated powder coatings achieve excellent aesthetic results while also prioritizing environmental friendliness and performance, providing more high-quality options for wheel coating.

1.3. Replacing Liquid Clearcoat

The application of powder clearcoat is well-established for wheel types requiring high surface finish, such as polishing wheels and precision wheels, with over 30 years of application history. Compared to water-based clearcoats, which have gained increasing popularity in recent years, powder clearcoat is more mature in terms of technical stability, application adaptability, and coating performance. In replacing traditional oil-based clearcoat, powder clearcoat demonstrates significant advantages. Oil-based clearcoat contains a large amount of volatile solvents, resulting in significant VOC emissions, while the zero-VOC characteristic of powder clearcoat perfectly meets environmental protection requirements. In practical industrial applications, the advantages of powder clearcoat also lie in cost control. Due to the high stability of the powder coating process and the uniform coating thickness, it is less prone to defects such as sagging and pinholes, resulting in a much higher yield rate than liquid clearcoat. This means that material waste and labor time lost due to rework of defective products are significantly reduced during the production process. Although the raw material cost of powder clear coats may be slightly higher than that of some liquid clear coats, the cost savings brought about by the overall improvement in yield rate mean that using powder clear coats will not lead to a significant increase in the company’s overall production costs. At the same time, it can significantly reduce VOC emissions, achieving a good balance between environmental protection and cost.

1.4. Replacement for Oil-Based Medium Paints

In the vacuum electroplating process for automotive wheels, the traditional process typically employs a complex process of “base powder + oil-based primer + oil-based medium paint + electroplating layer + clear coat”. Both oil-based primers and oil-based medium paints contain large amounts of solvents, resulting in not only high VOC emissions but also problems such as unstable coating adhesion and a narrow application window. The emergence of powder medium paints has successfully replaced the traditional “oil-based primer + oil-based medium paint” process and is increasingly becoming the mainstream choice for vacuum electroplating wheel coating processes. Powder coatings possess high saturation, forming a smooth and even coating base on the wheel hub surface, providing excellent conditions for the uniform deposition of subsequent electroplating layers. Their coating yield is also significantly higher than that of oil-based coatings, effectively reducing electroplating failures caused by coating defects. Furthermore, the zero VOC environmental friendliness of powder coatings completely solves the VOC emission problem associated with traditional oil-based coatings, bringing a revolutionary change to the wheel hub vacuum electroplating process. More importantly, in this application area, there are currently no mature water-based liquid paint products that can serve as a substitute. The application of powder coatings not only meets current environmental and production needs but also, to a certain extent, leads the technological development direction of wheel hub vacuum electroplating coating processes.

2. Superior Performance of Powder-Coated Wheels

2.1 Superior Scratch Covering

Aluminum alloy is one of the main raw materials for automotive wheels. During the casting process, aluminum alloy wheels often develop relatively rough casting textures on their surface, and may even have minor dents, scratches, and other surface defects. If these defects are not concealed, they will directly affect the appearance quality of the wheel hub. Powder coatings, being solvent-free, exhibit low volume shrinkage during curing, resulting in a denser coating structure. Furthermore, the powder particles effectively fill tiny depressions and gaps on the wheel hub surface, demonstrating excellent “filling and concealing properties.” Based on this advantage, powder coatings are often used as the first coating layer for wheels, effectively masking casting defects on aluminum alloy wheel surfaces, resulting in a smooth and even appearance. This lays a good foundation for subsequent coating applications, further enhancing the overall appearance quality of the wheel hub.

2.2 Better Stone Impact Resistance

During vehicle operation, wheel hubs inevitably experience impacts from road stones, gravel, and other debris. If the wheel hub coating lacks stone impact resistance, problems such as coating damage and peeling can easily occur, affecting not only the appearance but also exposing the wheel hub substrate and leading to corrosion. Traditional multi-layer liquid paint processes, due to the thinness of each layer and limited bonding strength between layers, are prone to coating delamination and peeling when impacted by stones. Powder coatings, being solvent-free, are less prone to sagging during application. By adjusting spraying parameters, a “single-layer high film thickness” coating effect can be easily achieved. Compared to complex multi-layer liquid paint processes, single-layer powder primer has a more uniform thickness and a more stable internal structure. When impacted by stones, it better absorbs the impact force, reducing the probability of coating damage and exhibiting superior stone-impact resistance, effectively extending the wheel’s lifespan.

2.3 Excellent Surface Performance

As the final step in wheel coating, powder clear coat plays a crucial role in the surface performance of the wheel. Regarding gloss and fullness, powder clear coat, through precise control of curing temperature and time, can form a high-gloss, mirror-like coating, giving the wheel a full and bright visual effect, enhancing its aesthetics and perceived quality. In terms of corrosion resistance, the dense structure of the powder clear coat effectively prevents corrosive media such as moisture, oxygen, and salt from penetrating to the wheel substrate surface, thus providing long-lasting corrosion protection. Compared to liquid clear coats, powder clear coats offer more stable corrosion resistance. Even in harsh environments such as high-temperature, high-humidity, and salt-spray-prone coastal areas, they maintain a good coating condition, effectively preventing wheel rim corrosion.

3. Conclusion

In summary, the application of powder coatings in automotive wheel rim painting not only meets the stringent national requirements for VOC emission control, replacing traditional high-pollution paint coating processes, but also reduces production costs for companies by simplifying the coating process, improving coating efficiency and yield. In terms of performance, powder-coated wheels exhibit significant advantages in terms of concealing properties, stone chip resistance, surface gloss, and corrosion resistance, meeting the high requirements for appearance quality and performance of automotive wheels. These outstanding advantages have led more and more wheel rim manufacturers to switch from traditional paint coating to powder coating. With the continuous innovation and development of powder coating technology, the application scope of Rim Powder Coating in the automotive wheel hub field will be further expanded in the future. Its advantages in environmental protection, performance stability and cost control will also become more prominent, making it the mainstream development trend in the automotive wheel hub coating industry.