Fluidized Bed Powder Coating
In contrast, fluidized bed powder coating is somewhat different. Here's how it works:
- Preheating: Parts are preheated to ensure the powder adheres effectively. It must reach a temperature of at least 350°F, ideally ranging from 400 to 450°F. This elevated temperature is essential to keep the part hotter than the melting point of the powder. Typically, a conventional gas-fired convection oven is used to achieve this preheating.
- Dip-Coating: The next step involves dip-coating the preheated part. An air pump facilitates the flow of air through the powder coating fluidizer, creating a fluid-like suspension of powder particles. The hot part is then immersed in this fluidized bed of powder coating and moved around to ensure a continuous coating.
- Submerging: The part remains submerged in the fluid bed to allow the powder paint to create a thick, wear-resistant coating. The final thickness of the coating depends on the initial heat of the object before immersion and the duration it spends in the fluidized bed of powder coating.
- Post-Fusing: The last phase of fluidized bed powder coating is the post-fusing process. After any excess powder drips off the product, it is transferred to an oven set at a lower temperature for curing. Importantly, the post-heat temperature must be lower than that of the initial preheating oven. This step ensures that all the powder adheres to the part during the dip and melts into a smooth, uniform coating. Using too high a temperature in the oven could lead to undesirable outcomes such as the coating melting off, sagging, or dripping.
Automated Optimizations for Powder Coating Application
Employing oscillators, reciprocators, and robots to manage spray equipment offers cost savings and ensures consistent coverage in numerous applications. Gun triggering, which involves automatically turning the spray gun on and off based on part positioning, reduces overspray, leading to reduced material consumption.
Significance of Grounding & Best Practices When Applying Powder Coating
Grounding is arguably the most important aspect of a successful powder coating application. We’re saying “arguably” because this is a subjective statement and for some other factors may be more important whether that be the spraying system or the powder itself.
From a safety perspective, ungrounded parts can accumulate charge, posing a risk of electrical discharge when approached. This discharge can not only be startling but also hazardous. Discharges across small distances between charged surfaces and ground can contain enough energy to ignite the powder being sprayed from the gun, further emphasizing the safety aspect.
On a quality level, maintaining a solid ground is crucial for achieving consistent film thickness and uniformity in powder application. Issues such as Faraday cage penetration and back ionization can arise without proper grounding. A study conducted by Kolene Corporation highlighted that maintaining an excellent ground during the powder application process significantly improved powder-coated surface topography.
Lastly, from a cost perspective, poor grounding adversely affects transfer efficiency and minimum film thickness. Inefficient grounding can result in excessive powder usage to achieve the desired film thickness, leading to increased waste and expenses.
To ensure effective grounding, it is essential to have a traceable path from the part to the powder coating earth ground rod, with no breakdown in electrical conductivity. Using an 8 to 10-foot ground rod, preferably longer in high resistivity soil conditions, and measuring resistance between ground rods can help ensure a reliable ground. Employing solid copper ground bars of appropriate length further enhances the effectiveness of the grounding system. Overall, proper grounding is a critical factor in achieving both safety and efficiency in powder coating applications.
Two Coat Powder Coating Application Process
What if you want to powder coat the same substrate twice? Well, that's exactly what the two coat process is. The two-coat process involves applying two coatings onto the same substrate, aiming to improve the finish's appearance while safeguarding it from environmental factors. This method, particularly prevalent in powder coating, presents various applications demanding precision and technique. Partial curing emerges as a pivotal technique, facilitating optimal crosslinking and adhesion between the coats.
So, how does the two coat application process work? First, the base coat undergoes pre-gelling at 392°F (200°C) for 2-3 minutes, ensuring superior inter-coat bonding. Subsequently, the substrate cools to 175-200°F (79-93°C) before applying the topcoat, followed by a full curing cycle. Common scenarios employing partial curing include primer with a topcoat for enhanced protection and clear coat atop a basecoat for aesthetic modifications. Specialized two-coat methods like Candies, Chromes, and Metallics necessitate adherence to specific curing parameters to achieve desired effects. Additionally, meticulous attention to timing and contamination prevention is imperative for optimal outcomes. Remember, consulting manufacturers and comprehending technical details are crucial for successful two-coat applications.
To grasp the intricacies of this process, delve into our detailed blog regarding the two coat process for insights and tips.
3. 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 ovenat temperatures between110 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.
Different types of curing ovens & significance and limitations of each
Convection Ovens: Convection ovens use a heat source (typically natural gas) and a fan to circulate heated air through an oven's duct. The hot air transfers heat to the part and the coating. This is the most common type of oven for powder curing. As the part reaches the desired temperature, it conducts heat into the coating, leading to powder curing.
Infrared (IR) Ovens: IR ovens use gas or electricity as an energy source to emit radiation in the IR wavelength band. This radiation is absorbed by the powder and the substrate directly beneath the powder without significantly heating the entire part. This approach enables a quicker temperature rise, causing the powder to flow and cure when exposed for a sufficient duration. However, curing uniformity may be influenced by the part's shape and density.
Radiation Curing Technologies: These include near-infrared, ultraviolet (UV), and electron beam (EB) processes. These technologies offer potential applications for powder coating on heat-sensitive substrates like wood, plastic parts, and assembled components with delicate features.
- UV Curing: Special powders are used that can cure upon exposure to ultraviolet light. These powders are initially heated, typically through infrared or convection methods, to a molten state. UV lamps then provide the energy to solidify the coating in a matter of seconds.
- Near-Infrared Curing: This method involves specially formulated powders, high-energy light sources, and precise reflector systems to complete the powder coating and curing process in a matter of seconds. It's particularly useful for heat-sensitive assembled parts.
Tips for improving your powder coating line
Generally, powder coating operation lines are measured on their efficiency, scrap/defects, and waste generated. Ideally, you’d want a high-speed operation line with minimal rework, and material wastage. So, with that in mind, here are some tips to help you get there and make the most out of your powder coating process.
- 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.
- Powder Management: Optimize powder storage and handling to prevent contamination and waste. Invest in efficient powder delivery systems and storage containers.
- Pre-treatment Process: Ensure thorough cleaning and surface preparation before powder coating. Proper pretreatment enhances adhesion and prevents defects.
- Quality Control: Implement a robust quality control process, including inspection, testing, and monitoring. Detect and address issues early to prevent costly rework.
- Powder Selection: Choose the right powder coating finishfor your specific application. Consider factors like color, finish, effects, durability, and substrate compatibility.
- Optimize Curing: Fine-tune curing oven settings to achieve the desired finish and performance. Monitor temperature and time to ensure proper curing.
- Training and Certification: Ensure your team is well-trained and certified in powder coating techniques. Continuous education improves skill levels and consistency.
- Waste Management: Implement effective waste management practices for overspray recovery and recycling of excess/residual powder.
- Customization: Tailor your powder coating line to meet the specific needs of your products and customers. Not every business is the same, which is why a customized setup is going to be the best fit for you to improve efficiency and operational quality.
- Safety First: Prioritize the safety of your team by providing the necessary protective gear and training. A safe working environment contributes to overall productivity.