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A guide to powder coating over an existing coating
Problem: Insufficient intercoat adhesion
Answer: You can powder coat an existing color.
However, there are many important factors to consider before doing so. This article explains,
what you need to consider before powder coating an existing coating and how you can powder coat the existing coating.
One of the biggest advantages of powder coating is its durability as a finish. This is one of the reasons.
A second reason you may not want to remove the existing coating is that you want a durable finish with as little additional cost as possible.
To better understand the pros and cons of powder coating as a process, you can read this guide here.
What you need to consider before powder coating over an existing finish:
In order to apply a powder coating over an existing coating, the underlying coating must be able to withstand high temperatures. Typically, powder coatings are cured at 250 to 400 degrees Fahrenheit, so the underlying coating and the part itself must be able to withstand high temperatures in order for the powder to cure.
You want to completely recoat the product - Because of the way powder coating works, you can't touch up spots on the product, you have to recoat the entire product.
You are comfortable with a thick film build - Powder coating typically has a build of at least 60μm, but for performance it is more common to have a build up to 250μm on the product surface
Similar to liquid coatings, the powder coating should be applied to a stainless substrate.
The coating is in good condition - The paint applied to the product should be free of bare spots on the surface and have good adhesion if the paint is flaking or bare spots are prevalent. You should not powder coat the coating.
The underlying coating is not excessively thick - If the existing coating is more than 60 - 80μm thick, it may be difficult to ground the product to effectively use a powder coating gun because it relies on electrostatic principles to apply powder to the product surface You may need to create a bare metal spot on the part to ground the part.
You may not get the same surface durability compared to stripping or sandblasting the product. Similar to applying a liquid coating, the quality of your surface preparation will largely determine the adhesion of your coating, which will also determine the durability of the coating. If you do not remove the entire coating and create a surface profile on the product, but instead create a profile over the existing coating, your powder coating may not last as long as you are more dependent on the bond between the original coating and the product surface.
A powder manufacturer may not be able to guarantee adhesion specifications. - If you are overcoating an existing coating, the powder coating manufacturer may not stand behind the performance of their powder. This must be verified with the powder manufacturer before coating an existing coating.
How to powder coat an existing coating
Step 1 - The first step to powder coating an existing coating is to visually inspect the coating to ensure that the underlying coating does not have bare spots, problems with significant peeling or rust fracture
Step 2 - If these problems are not present, you should roughen the surface by sanding. If they are present, you will need to prepare the surface by removing the old coating.
Step 3 - Clean the Product Surface - As with any coating application, you should clean the surface with an appropriate cleaner to ensure that no dirt or other surface contaminants are present before applying the new powder coating.
Step 4 - Select the correct settings for your powder coating equipment. - To apply powder to an existing paint, you will often need to adjust the powder coating equipment setting (usually using a lower KV setting than the typical KV setting for a new product surface). Often the powder gun has a selector switch for rework settings, or if not, KV settings between 20 and 50 KV should be used. In addition, you may need to increase the amount of powder used, as you need to make sure the surface is thoroughly covered with powder coating so you don't get a bad-looking finish
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