FAQ

Powder coatings are increasingly widely used in traffic guardrails. With economic development driving traffic problems, guardrails are frequently seen on highways, railways, and expressways. These guardrails are exposed to wind and rain for extended periods, thus requiring a protective film. Powder coating is the most commonly used coating for guardrails.

1. Classification by Application

1.1 Types of Traffic Guardrails

Traffic guardrails are generally classified by use, including highway guardrails, railway guardrails, airport guardrails, port guardrails, and urban road guardrails; by structure, including guardrails and corrugated beam crash barriers; by coating method, including powder-coated guardrails and dip-coated guardrails; and by the powder coating used, including thermosetting powder guardrails and thermoplastic powder guardrails. Generally, they are classified by use.

1.2 Highway Guardrails

Since the 1990s, my country’s expressway network has developed rapidly from scratch. By 2015， our country’s total highway mileage reached 4.56 million km, of which expressways accounted for 125.000 km. China’s expressway mileage has surpassed that of the United States, ranking first in the world. By 2030,our country will construct approximately 30.000 km of new expressways.

Expressways are characterized by full enclosure, high speed, time savings, fewer traffic accidents, and lower transportation costs. However, due to their high speed, it is essential to enclose and isolate the sides of the road to prevent interference from people, livestock, and other vehicles. Side enclosures are generally achieved using guardrails, and crash barriers are used on both sides of the on- and off-road lanes within the expressway. Additionally, anti-glare barriers are installed in the median. Currently, almost all guardrails are coated with thermoplastic powder coating, while most crash barriers are coated with thermosetting powder coating, although some corrugated beams use other powder coatings.

1.3 Railway Fences

Most railway fences are made of welded steel wire with a frame. To increase strength and safety, and for aesthetic purposes, some local railway bureaus have designed fences using flat steel pressed into irregular ribs and welded with rectangular steel pipes to resemble wrought iron. Railway fences are mostly coated with dark green thermoplastic powder. The posts are made of reinforced concrete using centrifugal casting, resulting in exceptional strength, while square tubing is also used.

1.4 Airport and River Port Fences

Airports were among the first to use PVC-coated fencing for enclosure and protection. my country has over 200 civil airports, and military airports also use fencing combined with razor wire mesh. Airports are the gateways to various regions, and the main thoroughfares leading to them are often enclosed with PVC-coated fencing. Ports, especially coastal ports, benefit from the corrosion resistance of PVC-coated fencing due to salt spray.

1.5 Urban Road Fences

Previously, urban road fences were simple in shape and had poor corrosion resistance. With the development of powder coating, PVC-coated fences are now widely used, especially in large and medium-sized cities. Currently, except for stainless steel fences, most are PVC-coated.

2 .Traffic Fence Powder Coating Equipment and Process

As a major type of traffic fence, fencing is widely used in highways, railways, airports, urban roads, and other fields. Due to their specific application scenarios, isolation fences have distinct characteristics in terms of size, shape, usage environment, and production volume. These characteristics directly determine the selection of their powder coating equipment and processes.

2.1 Product Characteristics of Isolation Fences

2.1.1 Large Size

To meet the needs of isolation and protection, isolation fences are typically large in size. Generally, the fence post spacing is set at 3m, and the fence height can reach approximately 2m. Each isolation mesh panel is mostly 3m × 2m. In some scenarios with higher protection height requirements, the height of the isolation fence can even reach 2.5m. The larger size means that the isolation fence requires more processing space and more suitable coating equipment during the coating process to ensure that the coating can evenly cover the entire surface.

2.1.2 Complex Shape

The structure of isolation fences is relatively complex. They typically use welded wire mesh or punched steel plate mesh as the face mesh, and are then supported and fixed with steel posts. Unlike flat, plate-like components, wire mesh structures have numerous intersecting nodes, and the connections between posts and mesh panels also have many gaps and corners. These complex structural parts are prone to creating blind spots in the coating process, placing higher demands on the uniformity and coverage of the coating.

2.1.3 Harsh Outdoor Environment

Isolation fences are primarily installed outdoors, exposed to the natural environment for extended periods. They must continuously withstand wind, sun, rain, and the freezing and thawing of snow and ice. Especially in summer, intense sunlight can significantly raise the surface temperature of the fence, and long-term ultraviolet radiation is a major cause of aging in organic coatings. Although organic coatings have good resistance to acids, alkalis, and salts, ultraviolet radiation can damage the resin structure in the coating, leading to cracking, discoloration, and peeling. Therefore, the anti-corrosion and decorative coating of the isolation fence must possess excellent weather resistance, and to enhance the protective effect, the coating thickness usually needs to be relatively thick.

2.1.4 Large Production Batch

With the large-scale advancement of transportation infrastructure construction, the market demand for guardrails is enormous. Often, production tasks requiring tens or even hundreds of kilometers of guardrails need to be completed within a short period, involving tens of thousands of product parts. This necessitates that the powder coating production line for guardrails possess high production efficiency, enabling continuous and stable batch production; otherwise, it will be difficult to meet the schedule requirements of engineering construction.

2.2 Powder Coating Methods for Guardrails

Based on the aforementioned shape characteristics, usage environment, and production batch requirements of guardrails, the current main method for powder coating guardrails is fluidized bed dip coating.

The principle of the fluidized bed dip coating process is to add powder coating material to the container of a fluidized bed equipment. By introducing compressed air from the bottom of the container, the powder coating material exhibits a boiling-like state under the action of the airflow, forming a fluidized bed. Subsequently, the pre-treated (e.g., degreasing, derusting, phosphating) fencing workpiece is heated to a certain temperature and rapidly immersed in powder coating in a fluidized bed. Because the workpiece temperature is higher than the melting temperature of the powder coating, the powder coating rapidly melts and adheres to the workpiece surface, forming a uniform and continuous coating. After the workpiece is removed from the fluidized bed and cooled to set, the entire dip coating process is complete.

This coating method has significant advantages:

First, fluidized bed dip coating allows the powder coating to fully cover the complex mesh structure and connecting gaps of the fencing, effectively avoiding coating blind spots and ensuring uniform coating coverage.

Second, by controlling parameters such as workpiece temperature and dip coating time, the coating thickness can be flexibly adjusted to meet the fencing’s need for thick coating protection.

Furthermore, the fluidized bed dip coating process is relatively simple to operate, has high production efficiency, and can adapt to the requirements of mass production of fencing. Simultaneously, the coating has strong adhesion to the substrate, excellent weather resistance and corrosion resistance, and can provide long-term reliable protection for the fencing.

3. Conclusion

The powder coating process for traffic guardrails mainly adopts fluidized bed coating, which is the preferred coating method for most powder coating manufacturers. Guardrails have very strict requirements for coating thickness, film adhesion, impact resistance, and other performance aspects, and fluidized bed coating is currently the most advanced coating method that best meets all these performance requirements.