Powder coating is widely accepted as the preferred finishing method for a wide range of applications. Liquid paint has several drawbacks such as rising costs, low quality finishes, and negative environmental impact. Due to these reasons, powder coating has emerged as an alternative to paint. But that is not to say that powder coating applicators don't face their challenges.
Big or small, every powder coating company faces issues with coating.
The powder coating process involves spraying of powder by an electrostatically gun onto a surface. Another method includes dipping the parts on a fluidized powder bed. The component is then heated in an oven to cure or melt the powder. During the curing process, the powder spreads uniformly over the surface and gives the component its desired features.
Problems with Powder Coating
Powder coating is made of pigments and resins, which can be coated on any surface to create durable, protective, and hard finishes. However, the process is complicated and requires proper equipment and expertise to complete.
Lack of experienced applicators or proper equipment may lead to issues in the final finish. These problems include:
Poor Adhesion
Poor adhesion of the powder particles is the most common issue in powder coating. Poor surface preparation, wrong choice of powder, or wrong curing parameters may cause improper adhesion.
Uneven Coating
Uneven coating is another major problem with powder coating. It occurs due to technical factors like wrong selection of powder, improper distance between the gun and object, or wrong electrostatic setting of the gun.
Poor Grounding
Poor grounding can be another setback during the powder coating process. Non-compliance with EFTA standards for grounding will not electrostatically charge the powder, no matter how much you fiddle with your gun settings. Improper grounding will lead to your powder not being charged.
Faraday Cage Effect
Objects with odd geometry or an improper shape are hard to coat. That is because when electrostatics travel through the metal, these areas won't be coated easily. This is known as the Faraday effect. The powder pulls away from these edges and moves to smoother and uniform areas. As a result, these areas won't be powder-coated and may be susceptible to corrosion.
kV Rejection
Every object has a threshold to accept a charge. Over that amount, it starts to reject the charge and causes the coating to behave awkwardly. Upon curing, these defects are imminent. kV rejection also results in back ionization, which can form several unpleasant appearances.
Other issues with powder coating can be inconsistent powder feed, poor spray pattern, or poor thickness and coverage.
Solutions to Powder Coating Problems
The good news is - each issue mentioned above can be solved with the right process and application. Let's take a look at the fixes to the above problems:
Poor Adhesion
Proper pretreatment of the object, and using the right powder and curing parameters can solve poor adhesion issues.
Uneven Coating
Uneven coatings may result from incorrect powder gun settings, improper distance between the gun and the object, and wrong powder type. An expert operator can identify the cause of uneven coating and provide precise services with the desired finish.
Poor Grounding
The first step to resolving grounding issues is to ensure you have a good earthen ground. Check for proper connection between the substrate and the earthen ground. You can use racks or hangers for the same.
Also ensure that your substrate is properly clean, as unclean parts won't let the charge pass through easily. Grounding issues can be solved with proper maintenance and cleaning procedures.
If the issue is with gun settings, check the powder flow and ensure that the part to be coated is getting the requisite amount of powder. If you cannot match the settings to the desired application, check the technical data sheet of your gun or check with your supplier for proper flow settings.
Faraday Cage Effect
There are a few reasons for the Faraday Cage effect. Let's start with gun-to-object distance. Make Sure you spend time with your gun, especially its positioning about the object. Faraday Cage areas cannot be filled by pressing the gun to the inadequately painted areas. It could be possible that the tip of the gun has worn out, so ensure to check and use your device consistently to gain expertise.
Next comes powder flow defects. If inadequate amounts of powder leave your gun, coating internal corners can be tricky. In this case, adjust the flow and amount of powder leaving your gun.
Lastly, if the powder is too fine, it won't be able to carry the required charge - thus increasing Faraday Cage risk. Ensure to use the right powder for the desired application.
kV Rejection
Once again, check for proper grounding in case of kV rejection. You can also reduce kV settings or the powder flow to reduce the load and voltage on the substrate.
Wrapping Up
Issues with powder coating application can happen at every job shop. Moreso, every operator faces such setbacks at least once in their career. While such powder-coating defects can be annoying; they can be corrected.
As we have gathered, most of the time, it's rectifiable issues like grounding, object-to-gun distance, and the powder flow leaving the gun. All these can be adjusted to ensure the powder adheres to the surface and spreads uniformly.
Lastly, always keep your equipment clean. Preventive maintenance will reduce error chances and result in a flawless finish every time.
At Rusty Lions, we have been through it all. From kV rejection to the Faraday Cage effect, we have seen it all. Leverage our two decades of experience in powder coating all kinds of metal and non-metal surfaces.
