Ask the Experts—November/December 2024

You have questions, we have answers. In each issue of PCT, our extensive network of powder coating experts provides information to help you with your powder coating challenges. Let us know what’s keeping you up at night and we’ll do our best to help you get a good night’s sleep!

Bath Time
Q: We have been operating our powder paint line for several years. Like most companies, we have been running the line but have now had some turnover and training has become more difficult. Someone asked if we had documented standard operating procedures for our pretreatment system. However, these feel burdensome. Why are they important to our powder coating process?

A: Standard operating procedures (SOPs) are essential for maintaining the quality and safety of your chemical baths. These procedures should be developed in collaboration with your chemistry supplier and tailored to your specific system capabilities.

SOPs outline the manufacturer’s intended use of their products and provide guidelines for assessing material quality. Testing standards may include parameters such as color, smell, pH, viscosity, and titration to determine the correct solution concentration. It’s crucial for paint and pretreatment suppliers to offer regular training for operators and managers to ensure everyone can perform, interpret, and respond to test results effectively. Maintaining records of these results may also be required by customer or manufacturing auditors.

Routine parameter testing is vital for maximizing product effectiveness. If results fall outside recommended limits, specification testing serves as an early warning, enabling prompt corrective actions. Adhering to SOP parameters also promotes workplace safety. Using chemicals beyond their specified range can create hazardous conditions. For instance, chemicals used in metal pretreatment often contain reactive acidic or alkaline substances. Maintaining the stability of these products ensures proper substrate processing and a safe work environment for employees.

A: Transitioning from liquid coating to powder coating can indeed present a learning curve. Repairing defective powder coating can sometimes be costly, so your first step should be to evaluate whether the part is worth repairing or if it should be scrapped. If repair is the most viable option, selecting the appropriate method is crucial for achieving a satisfactory result.

If the defect is a large area, the best method would be to strip the entire part. This can be accomplished via blasting, chemical stripping, thermal stripping, or with a fluidized sand bed. After the part is stripped, then the part can be coated as if it was a new part. If it is a small spot repair, the defect can be sanded to a feathered edge, wiped clean with water or a solvent, and recoated.

If you encounter any specific challenges or unique issues, consulting with the powder coating manufacturer or a professional in the field can provide additional guidance.

Thermophobia
Q: Our company is introducing a new product made with a lightweight plastic composite material. We want a finish that is both protective and decorative. We are very sensitive to environmental, climate, and cost of energy issues and have ruled out solvent and water-based paints. The material will deform at 280 degrees Fahrenheit, so thermoset powder coatings are not an option because of high melt temperatures and long melt times. Is ultraviolet (UV) cured powder coating a possible finishing material for our product?

A: The key question to ask is, “At what temperature does the material begin to deform?” If this temperature is below 140 degrees Celsius (280 degrees Fahrenheit), you have what is typically referred to as a heat-sensitive part, which can be made from wood, plastic, composite, carbon fiber, or an assembled component with seals and/or liquid fluids. When you cure UV powder it is first melted in an IR oven, but the part does not heat like it would in a convection oven because it does not require extended dwell time to get the part up to temperature. The IR heats up the powder itself to melt it and then the part passes through a UV light to cure it. Because of this, you should not reach the heat threshold that would cause part deformation. As such, you should proceed with the test trials to make sure it will meet your other performance requirements.

The first trial involves testing adhesion to determine if the applied UV-cured powder passes either an X scribe or crosshatch adhesion test. If it does not, then test and evaluate various pretreatments and/or conductive primers. Once the adhesion test is passed, proceed to evaluating other physical properties as well as the finish appearance to determine if the UV powder meets the customer’s requirements.

The Space Between
Q: We are preparing to manually powder coat 16-foot long, 4-inch x 4-inch square tubes, currently spaced six inches apart. To maximize efficiency, we’re considering reducing the spacing to four inches, allowing us to hang an additional tube and increase throughput. However, before making this change, we need to ensure it won’t affect the quality of the powder coating. How can I determine if four inches is okay other than running them through the line? Is there a formula or rule of thumb that could be referenced to help figure this out? We have not yet powder coated these tubes, but we plan to do so soon. How does one learn, know, or test how the Faraday effect may occur on parts to be powder coated?

A: Typically, the recommended spacing rule for powder coating is between one and one and a half times the width of the part. Given that your square tube has a diagonal width of approximately 5.65 inches, the current six-inch spacing falls within this guideline. To determine if reducing the spacing to four inches is feasible, you will need to conduct testing. This process will likely involve some trial and error to find the optimal spacing that balances efficiency with coating quality. Keep in mind factors like ease of coating and uniform film thickness when parts are closer together. If reducing the spacing allows for an additional tube without causing other issues, it could potentially improve total part throughput. However, it’s crucial to monitor and adjust parameters such as voltage (max voltage recommended, set current to max), air pressure (set low to avoid surging), and powder delivery percentage to maintain coating quality. Lastly, a slower coating process is recommended to allow for adequate film thickness build-up while minimizing operator fatigue, given the length of the tubes.

The Yachting Life
Q: Our company powder coats stainless steel rods used on yachts. After powder coating, we cover the parts with black foam over the ends and high-contact points (such as stanchions and sharp bends), and then with a type of shrink wrap. When our customer receives the parts, some are stored inside their building and some outside. We’ve noticed an issue with the powder coating taking on the texture of the foam or plastic wrap on parts stored outside. We are using a TGIC powder coat material. Since this customer is storing the parts outside and is located along the southeast coast of the United States, I can’t help but think something could be getting introduced without their knowing that could be causing some type of reaction. Can you help point me in what might be causing this to happen?

A: Given that these parts are stored outdoors along the southeast U.S. coast, it is conceivable that environmental factors or materials used in the packaging might be contributing to this issue. Plastic wrap, when exposed to heat and humidity, will often leach out plasticizers onto the metal substrate and in this case, onto the powder coating. It would be recommended to consider a different type of covering or a paper wrap layer before the plastic wrap.

Compatibility Quiz
Q: Recently, we started coating parts from a new customer using new powder and have been having some issues and rejects. Prior to this, we had good quality parts. Can you point me to anything to help me understand what is happening? Any help would be greatly appreciated.

Survey Says
Q: I am updating a risk survey for a powder coating operation which had previously received a recommendation for increasing the water density discharge of the sprinkler system in a small area (324 ft2) of shelf storage to 7 feet high of 50-pound boxes of powder, citing NFPA diamond ratings. I am having difficulty finding the justification in the codes to require this sprinkler upgrade. I’ve been through NFPA 13 and NFPA 654, looking for storage guidance, but have come up short. I found a reference in the Fire Protection Handbook that powders are not customarily classified as hazardous and are commonly stored under ordinary combustible materials. Just wondering if you have had this topic come up before and have some relevant info at your fingertips.

Have a question for our powder coating experts? Send it to asktheexperts@powdercoating.org.