What Causes Pinholes in Powder Coating and How to Prevent Them
Powder coating, albeit being a reliable and cost-effective surface preparation and finishing technique, comes with its fair share of problems. One of the most common complaints we hear is the appearance of pinholes on the surface. While this is a common occurrence, it’s very much preventable. 10X Engineered Materials offers reliable solutions for helping to prevent pinholes in powder coating processes that are related to surface preparation.
What Is a Pinhole?
A pinhole is a small, circular, crater-like void that appears on the surface of a powder-coated part. It is one of the most common problems in powder coating and is often caused by oil contamination, moisture, outgassing, and curing mistakes.
The appearance of pinholes on powder-coated surfaces could indicate a need for repairs before proceeding with recoating. Minor pinholes require sanding and refilling of the affected area, followed by the reapplication of coating. Bigger holes, however, may require powder coat stripping, reblasting of the substrate, and powder coat reapplication.
Common Causes of Pinholes
Several factors can cause the appearance of pinholes on the surface of materials. Below are examples of what causes pinholes in powder coating:
- Outgassing: Outgassing occurs when substrates under the powder release gases during the curing process. These gases escape through the powder coat, forming pinholes in the material.
- Surface contamination: Failing to clean the surface thoroughly before powder coating can lead to contamination. Oil, dirt, and grease may be left on the surface and trapped by the powder coat. When exposed to high heat, these contaminants turn into gas, bursting out of the coating and creating pinholes.
- Galvanization: When steel is coated with zinc during manufacturing, the zinc layer can trap gases, which then turn into pinholes during the powder coating process.
- Coating thickness: Each layer of powder coating should be applied very thinly, even if the project requires a thick one. Applying a thick layer straight away can affect the curing process and cause gases to appear on the surface, creating unwanted pinholes.
- Castings: Powder coating projects often use cast metal for the base. However, cast metal can produce gases during the powder coating process and trap them inside, leading to pinholes.
Best Practices to Prevent Pinholes
A powder coating pinhole problem can impact your project’s overall quality and the part’s functionality. For optimal results, note these best practices in preventing pinholes:
Adequate Surface Preparation
Surface preparation is crucial in powder coating processes, especially in avoiding issues like pinholes. The substrate or surface to be powder coated must be thoroughly cleaned and blasted; if there is an inadequate profile, you can have adhesion challenges, whether through blasting, washing, or applying chemical treatments. Surface prep eliminates contaminants like oil and grease. Depending on the amount of “dirt,” you may need to preheat metal or use alcohol to remove debris.
Substrate Preheating
Pinholes can be prevented by properly preheating or outgassing the substrate to the curing temperature before applying the coating. This allows gases and contaminants trapped in the metal to escape before being trapped under a layer of powder coating, leaving nothing to disturb the coating in the curing process.
Contaminant Elimination
Ensure you’re using clean and dry compressed air during the powder coating process to avoid contamination. If you haven’t already, equip your system with an air filter to avoid powder coating issues due to dirty compressed air. This step also applies to your powder spray booth and curing ovens. Avoid spraying lubricants, anti-corrosives, and pretreatments close to your booths and ovens.
Proper Training and Education
Knowing how to prevent pinholes in powder coating requires having a working knowledge of your materials and equipment, as well as understanding the entire powder coating process.
Proper training and education from experts teach you about the intricacies of the materials you work with. For example, different powders have different curing times. Knowing this helps prevent problems like pinholes and saves you time and resources from having to redo the project.
Choosing the Right Sandblasting Material
Surface preparation is crucial in achieving excellent powder coating results. One reliable and effective surface preparation method is sandblasting. Choosing the right sandblasting abrasive for your needs is vital in preventing some of the most common causes of powder coating pinholes. Here’s what to consider:
- Surface finish
- Safety
- Operational efficiency
- Reusability
- Eco-friendliness
- Adhesion strenght
Superoxalloy is one of the only biosoluble abrasives on the market, developed for safe and efficient surface preparation. It’s a cost-effective sandblasting solution that effectively removes contaminants, old coatings, and corrosion. EpiX is a line of superoxalloy fine abrasive media that generates low amounts of dust, making it a nonhazardous and more environmentally sound choice for powder coating processes.
Eliminate Pinholes When You Blast With EpiX
Pinholes are among the most common issues in the powder coating process. They often occur if you miss essential steps, especially surface preparation. To avoid pinholes forming on your material, sandblasting with a top-quality abrasive is highly recommended.
EpiX is a fine blasting abrasive suitable for a wide range of industrial applications, such as powder coating. With it manufactured in three profile ranges, you can find which type is best for your sandblasting and powder coating needs. Shop EpiX online or contact 10X Engineered Materials for more information.
