Powder coating stands as one of the most recent advancements in surface finishing techniques popular today. It emerged as a novel finishing method during the 1960s and has since become the leading choice among coating systems due to its environmentally friendly benefits and solvent-free composition. This technology can achieve a coating thickness of approximately 2-4 mils with a single coat, demonstrating exceptional efficiency in material usage.
Powder coating delivers robust mechanical properties and exceptional edge protection, ensuring that the finished product retains its integrity and appearance. Notably, this finishing method consistently yields optimal results with just one application. Additionally, it minimizes waste through its remarkable overspray recovery rate, which can reach up to 95%. Overall, powder coating proves to be a cost-effective choice, benefiting both the environment and your budget by reducing material and application expenses.
How does Powder Coating Work？
The powder coating is usually done by electrostatic spray deposition (ESD) or fluidized-bed application. Both two methods provide great gloss levels, textures, various colors, and high-quality surfaces, making them used on a variety of products, including medical devices, architectural applications, automotive, and even fiberboard avionics.
Different types of powder coating substrates
The choice of substrates plays a crucial role in determining the final finish, durability, and suitability for a wide range of applications.
Here, we do more coat for Steel.
Steel structures are one of the most popular substrates for powder coating. It’s durable, strong, and versatile, making it a prime choice for various industries. Powder-coated steel is commonly seen in automotive parts, appliances, outdoor furniture, and industrial equipment. Its ability to withstand harsh environmental conditions, such as exposure to UV rays and moisture, makes it a reliable option.
When selecting the right substrate powder and powder coating, it is necessary to consider factors such as substrate type, environmental conditions, application field, coating performance, aesthetics, process conditions, environmental protection and cost. We will consult the powder factory according to the situation, buy the appropriate powder, and make samples, and do reliability tests. Only in this way can the quality, durability and aesthetics of the coating be ensured to meet the needs of practical applications.
Did you know that there are multiple different types of powder coating, and that some are better suited than others for the finish you require? Here’s a quick rundown on the various types of powder coatings:
- Epoxies: the first widely used powders, epoxies adhere to the surface of the item being coated very well. Unfortunately, they make up for their incredible adhering power with a lackluster performance in durability.
- Polyesters: these are the most commonly-used powders, and you get great value for your investment with them. They also come in a huge array of colors, gloss levels, and special effects!
- Super Durable Polyesters: these offer all of the great advantages of polyesters with the additional benefit of holding their color and gloss for 10 to 15 years.
- Epoxy-Polyester Hybrids: These combination resins boast overbake resistance and yield ultra-smooth, thin films. They’re also more economical than a pure epoxy.
- Fluoropolymers: These powders offer extraordinary weathering properties and world-class color and gloss retention. They are often used on architectural projects.
- Urethanes: Chemically similar to polyesters, but these powders use a different curing agent, and offer a very smooth finish paired with good durability.
Powder Coating Process
The powder coating mechanism is divided into different stages that are essential for smooth and high-quality work. The whole working process can be divided into three steps.
- Pre-treatment
- Application of Powder Coating Method ( electrostatic spray deposition )
- Oven Curing
Pre-treatment & Surface Preparation
Before applying the powder, the substrate must undergo thorough cleaning to remove any contaminants like oil, grease, or rust. This crucial step ensures proper adhesion and a flawless finish. The substrate is freed from dust, scale, rust, grease, dirt, and any oxide layers (for example on aluminum). There exist chemical and mechanical pre-treatment processes. To increase the corrosion protection and improve the adhesion of the powder coating a conversion layer is created on the piece during the pre-treatment. Following this, the workpiece must dry completely.
Cleaning Methods: The cleaning process involves the use of weak alkali and neutral detergents, often in dip tanks or wash stations. Bulk products are usually silanized by spraying on the assembly line, and for larger products, phosphating is used in dip tanks.These stations are equipped to spray parts with hot water, steam, detergents, and other pretreatment solutions to clean and chemically prepare the surface before coating. They ensure a spotless foundation for your powder coating.
Spray Dip Tank
|
Spray materials |
Pre-processing facilities | 1. Each link must pass through eco friendly phosphating (environmental protection phosphorization treatment) | |
| 2. Predefat / skim | Oil removal, dust removal | ||
| 3. Main defat | Remove the defat agent | ||
| 3. Water treatment I | Oil removal, dust removal | ||
| 5. Water treatment II | Remove the defat agent | ||
| 6. Silane Ceramicizing | Silane ceramic to enhance powder adsorption | ||
| 7. Wash I | Desilane ceramic agent, clean, rust prevention | ||
| 8. Wash II | Clean with pure water and prevent rust | ||
Pre-treatment processing
Masking Methods for Precise Applications: Sometimes, parts require specific areas to remain uncoated. This is where masking products like masking dots come into play. They’re available in various shapes and forms, generally constructed of paper or plastic film coated with a pressure-sensitive adhesive. These nifty tools adhere to the substrate, safeguarding the covered areas from meeting the powder material during the coating process.
Masking Methods for Precise Applications
Mechanical Pretreatment for Tough Contaminants
Mechanical pretreatment uses abrasive media, such as sand or shot blasting, to remove inorganic contaminants like rust, mill scale, and laser oxide from substrates. This method polishes or cleans surfaces and creates an anchor pattern that improves powder coating adhesion. Different abrasives are used based on the desired finish and contaminant removal needs; for example, walnut shells for de-burring, plastic grit for paint removal, and glass beads for a matte finish. While mechanical cleaning enhances adhesion, it does not provide corrosion protection. Therefore, a suitable primer, often zinc-containing, is applied post-blasting for added corrosion resistance.
Powder Coating Method Of Electrostatic Spray
ESD is the more common method, particularly for coating metal parts. The powder is applied using a spray gun, creating an electrostatic charge that draws the particles to the grounded substrate. This attraction results in a uniform and efficient coating. It is essential to avoid the entry of dust and dirt at this step. The powder spray gun creates a charged cloud of powder. As a result, the paint particles adhere electrostatically to the piece and form a layer.
Our Electrostatic Spray Powder Coating Production Line
In the electrostatic deposition method, the charged powder particles are deposited on the workpiece by the electrostatic process, The application process of an electrostatic charge spray gun, a powder feeder, and a powder spray unit, The electronic spray gun is both operated manually or through computer numerical control and it gives charge to the powder through the HIT generator. When the application process starts, the electrostatic spray gun starts spraying negatively charged powder.
Curing
After application, the coated substrate is subjected to high temperature curing in an oven. During this process, the powder particles melt and fuse, forming a robust and durable finish. The powder coating is cured in an oven at temperatures between 110 and 250 °C. Various factors such as heating time and substrate thickness affect the final curing time. Thermoset powder coatings require specific heat energy and time to trigger the chemical reaction needed for cross-linking into a film. When exposed to heat, the powder material melts, forms a smooth film, and starts to cross-link, eventually reaching full cure. Different methods can be employed to provide the necessary energy for curing.
If the curing temperature and time do not meet the requirements, which will cause the adhesion of the powder to deteriorate.This is not only related to the powder itself, but also related to your product, where the wall thickness is larger, the problem of insufficient temperature and poor powder adhesion is more likely to occur.
Once the powder is cured, you need to inspect your powder coat finish for any imperfections.
Tips for improving your powder coating
- Equipment Maintenance: Regularly maintain and clean all equipment, including spray guns, booth filters, and curing ovens. Proper maintenance ensures consistent performance and extends the life of your machinery.Especially when spraying white, the furnace ash on the line will fall up, affecting the beauty .
- Pre-treatment Process: Ensure thorough cleaning and surface preparation before powder coating. Proper pretreatment enhances adhesion and prevents defects.
- Optimize Curing: Fine-tune curing oven settings to achieve the desired finish and performance. Monitor temperature and time to ensure proper curing.
- Identify the product: Whether the product can be heated evenly, some product characteristics such as plate thickness and solid parts, resulting in insufficient temperature in some areas, the adhesion in most areas is good, and the adhesion in a small part of the area is poor.
- Powder Selection: Choose the right powder coating material for your specific application. Consider factors like color, finish, effects, durability, and substrate compatibility.White powder can not be curing for too long, easy to change color to be yellow.
FAQS
Compared to other coatings what advantages of powder coating
Powder coatings are solvent-free, environmentally friendly and safe to operate, but liquid coatings can dry at room temperature and are suitable for materials that are not resistant to high temperatures.
Compared with electrophoretic coating, electrophoretic coating has advantages in corrosion resistance and coating uniformity, but powder spraying has more advantages in process speed and environmental protection.
Spray paint is suitable for small batch and complex pattern painting, but powder spray has more advantages in mass production and environmental performance.
How do we make sure we get good quality
We will test the sample before mass production, and according to your product characteristics, do the reliability test, salt spray test, impact test, adhesion test and so on
Salt Spray Test
