1. Introduction
During powder coating, various minor issues inevitably arise—such as poor powder fluidization, insufficient coating hardness after curing, or unexplained discoloration of the coating. These problems not only affect construction efficiency but also lower coating quality, causing headaches for many practitioners. In fact, the root causes of these problems mostly lie in equipment parameters, operating procedures, or the materials themselves. Once the cause is identified, the problem can be quickly solved.
This article addresses these three most common problems, breaking down the core causes behind each and providing simple and easy-to-implement solutions to help you avoid detours and make the spraying process smoother and the coating quality more stable.
2. Poor Powder Fluidization
The powder fluidization state directly affects the powder application rate and coating uniformity. Poor fluidization easily leads to uneven powder distribution and inconsistent coating thickness. Common causes and solutions are as follows:
2.1 Insufficient Compressed Air Pressure
Compressed air is crucial for driving powder fluidization; insufficient pressure will prevent the powder from being fully suspended.
Solutions:
First, check if the compressed air supply is stable. Clean the air filter (to prevent impurities from clogging and affecting air pressure). Then, adjust the pressure appropriately according to equipment requirements to ensure smooth airflow for powder fluidization.
2.2 Microplate Clogging
The microplate in the powder supply tank is crucial for airflow distribution. If clogged by ultrafine powder, oil, or impurities in the compressed air, it will lead to uneven airflow distribution and poor fluidization.
Solution: Stop the machine and check the microplate. If clogged, clean or replace it promptly to ensure uniform airflow through the microplate and suspend the powder.
2.3 Powder Moisture Absorption
Powder left in the supply tank for extended periods easily absorbs moisture from the air, becoming damp and clumpy, affecting fluidization.
Solution: Increase the atmospheric pressure appropriately and fluidize the powder for an extended period, using airflow to remove moisture. If moisture absorption is severe, gently stir with a clean tool to assist fluidization and accelerate moisture evaporation.
2.4 Powder Clumping / Overfilling
Improper powder storage can lead to clumping, or overfilling the powder supply hopper, both of which obstruct airflow and result in poor fluidization.
Solution: If powder clumps, manually loosen the clumps first, then filter out impurities and hard lumps using a sieve; control the powder filling to two-thirds of the fluidized bed volume, leaving sufficient space for airflow circulation to ensure adequate fluidization.
3. Poor Surface Hardness After Curing
Insufficient hardness after curing makes the coating prone to scratches and wear, directly affecting the product's protective performance and service life. Common causes and solutions are as follows:
3.1 Incomplete Curing
This is the most common cause. Insufficient baking temperature or time will prevent the coating from fully curing, resulting in insufficient hardness.
Solution: According to the technical requirements of powder coatings, appropriately increase the baking temperature to ensure the specified curing temperature is reached; if the temperature is met but the hardness is still insufficient, extend the baking time to allow the coating to fully cross-link and cure.
3.2 Over-curing
Conversely, under-curing, excessively high baking temperatures and prolonged baking times can lead to coating embrittlement and a decrease in hardness.
Solution: Adjust baking parameters promptly, appropriately lowering the temperature and shortening the baking time to balance curing effect and coating toughness, avoiding over-curing that causes embrittlement.
3.3 Slow Baking Rate
Slow heating causes leveling agents to migrate prematurely to the surface during the melting and flow process, affecting the coating's cross-linking density and thus reducing hardness.
Solution: Increase the baking heating rate to allow the workpiece to quickly reach the set curing temperature, reducing the impact of agent migration on coating hardness.
3.4 Powder Quality Issues
If the above parameters are adjusted correctly but the hardness still does not meet the standard, the powder formulation is likely problematic.
Solution: Contact the powder supplier immediately, report the problem, request formula improvement, and replace with qualified powder coating.
4. Coating Discoloration After Curing
Coating discoloration directly affects the product's appearance. Common discoloration issues include yellowing, darkening, and uneven color. The core causes and solutions are as follows:
4.1 Improper Baking Parameters
Baking temperatures exceeding the powder coating's tolerance range, or baking times that are too long, can lead to thermal aging of the coating, resulting in discoloration and yellowing.
Solution: Strictly adhere to the recommended parameters for the powder coating, lowering the baking temperature or shortening the baking time to prevent discoloration due to thermal aging.
4.2 Uneven Coating Thickness
Inconsistent coating thickness will result in variations in color depth after curing, appearing as "discoloration."
Solutions: Check and adjust step by step:
① Check the position and direction of the spray gun to avoid insufficient powder application in certain areas due to the Faraday effect;
② Adjust the production line speed or the spray gun vibrator stroke to match the powder output of the automatic spray gun with the conveyor speed;
③ If the airflow in the powder spraying chamber affects the powder spraying range, contact the equipment supplier to optimize the airflow design;
④ Check the powder supply and spray gun systems to ensure uniform powder fluidization and atomization;
⑤ Check if the high-pressure output is stable. If unstable, repair it promptly to avoid uneven powder application due to high-pressure fluctuations.
4.3 Unclean Air in the Oven
If the heating system in the oven contains oil, impurities, or if ventilation is poor, these contaminants can adhere to the coating surface, causing discoloration.
Solutions: Check the air heating system and clean away oil and impurities; check the ventilation system to ensure smooth airflow in the oven and promptly remove volatile impurities to avoid contaminating the coating.
4.4 Powder Formulation Issues
Some powders may also discolor under normal curing conditions due to unreasonable formulation design.
Solution: Contact the powder supplier, report the discoloration, request an investigation into the formulation, and request a replacement powder product.
5. Summary
The troubleshooting logic for issues like fluidization, hardness, and discoloration encountered in powder coating is simple: First, check the equipment status (e.g., compressed air, spray gun, oven), then adjust process parameters (e.g., air pressure, baking temperature/time, production line speed). If all are fine, then check the quality of the powder itself.
In daily construction, it is recommended to perform regular equipment maintenance (e.g., cleaning filters, checking spray guns), strictly follow the powder's recommended parameters, and properly store the powder (moisture-proof, avoid clumping). This can significantly reduce the occurrence of problems. If you encounter complex issues, contact the equipment or powder supplier promptly for more efficient problem resolution.
Remember, most coating problems are not "intractable diseases." With patient troubleshooting and targeted solutions, you can ensure coating quality and smoother production!
