How to Spray and Apply Multiple Coats of Powder Coating – A Complete Guide
As a powder coater, you may need to apply two coats for a variety of reasons whether for protective reasons or appearance applying a second coat of powder is important to know how to do well. In this guide, we cover practical tips on how to successfully apply multiple coats of powder to a product with great results. Ultimately adding one additional coat over an existing powder coating should be relatively easy but if you will be adding a multitude of powder layers it can become more difficult to apply the powder effectively depending on the quality of the powder gun you have.
Tip 1 for Applying Multiple Coats of Powder Coating – Understand Powder Coating Guns KV, Micro Amp, and Powder to Air Settings
KV stands for kilovolts and is a measure of the amount of energy that your powder coating gun delivers. Typically a higher KV setting will result in better powder attraction. The problem with high KV settings on a second coat application is that the product can have areas that are covered reducing the ability to find a grounded surface when applying the second coat of powder creating uneven powder application and an issue called back ionization. To overcome this issue related to a second coat powder application you typically will reduce the KV setting you are using to apply the second coat of powder at. In addition, if your powder unit offers independent control of microamps typically micro amps will be turned down low to help reduce issues with back ionization. If you only can set KV’s then just reduce the KV setting on the second coat. If your powder gun is a very low-cost one, then you may not be able to reduce KV’s or microamps which is one of the main reasons you may want to consider upgrading your powder coating gun (more on powder coating gun prices and why they vary here). You will also want to turn down your powder to air volume and hold the powder gun a bit further back from the surface of the part with your powder gun on your second coat of powder coating.
Tip 2 for Applying Multiple Coats of Powder Coating – Use a Grounding Rod
As we already mentioned the second coat of powder coating causes problems with being able to have even application of powder on the product. However by using a grounding rod you can improve the overall ground of the product and by doing so make it easier for a powder to find ground evenly across the product surface on your second application of powder coating.
Tip 3 for Spraying Multiple Powder Coats – Partially Curing the First Coating and all Coatings Other than the Final Top Coat (Unless Spraying Chrome as the First Coat of Powder)
When applying multiple coats of powder coating you can have issues with getting good adhesion between coats (a problem known as inter-coat adhesion). This can cause premature coating failure unless properly addressed. To properly address problems with inter-coat adhesion you should partially cure each coat of powder prior to applying a powder coating over the first coat. Typically you will set the amount of cure time to be about 50 – 60% of the time of total cure so if your powder calls for being cured at 400 degrees for 20 minutes you would set the time for 10 – 12 minutes approximately (you will start timing after you confirm the whole part has reached the proper temperature with an infrared thermometer). After the coat has partially cured you can remove it from the oven and allow time for it to cool down to room temperature. In between coats, it is best to use gloves when handling the partially cured powder on the part and try not to have to wipe it down or blow it off as this can create a static charge which impacts applying the next layer of powder.
Overview of Spraying Multiple Coats of Powder Coating
- Apply an initial coat of powder using regular KV settings (usually as high as possible )
- Cure part partially in oven starting time from the moment the entire part reaches the proper surface temperature. The only exception is with chrome powder you will fully cure the chrome prior to any additional coat of powder is applied.
- Use clean gloves and remove the part allowing it to cool to room temperature
- Ensure the ground has been directly connected to the surface not over top existing powder and you are using a grounding rod
- Shoot a second coat of Powder with lowered KV’s lower powder to air mix and reduced micro amps – repeat steps of a partial cure for additional coats or if final coat fully cure the powder for entire time required
Ultimately applying multiple layers of powder coating can be done well as long as you follow a good process. By understanding ideal settings for your powder coating gun, oven cure times, and product grounding you can be sure to achieve good results applying multiple coats of powder coating.