As a former powder coat sprayer of over 25 years, I wanted to share my experience and insight into this form of paint spraying which is widely used in the sign industry and offered at Butler Signs.
Powder coating is one of the quickest and cheapest forms of paint spraying and also one of the strongest and most durable.
Where wet spraying has to be built up over layers, powder coating is a whole different ball game. A process called 'Electrostatic Spray Deposition' (ESD) is used, where a spray gun applies a positive electrostatic charge to the powder particles, which in turn create a powder film to the earthed (negatively charged) metal surface.
To achieve a good, even all over coverage it is important that it has good earth. This can be created by making sure that any hanging equipment ie: hooks are clean and conductive or even by holding an object while powdering. During the spraying process it is possible to get arcing and small electrical shocks, but these are minor and cause no lasting effects.
The amount of powder sprayed can depend on several factors ie: size, shape, weight and condition of metal. For example a new flat aluminium panel would require a lower amount of powder than something like an iron gate which could potentially be rusty. In this scenario there are several options to getting the best finish. These would include: sanding, shot / sand blasting, powder flooding or hot coating (which I will come to later on).
The amount of powder sprayed is measured in Microns. Only when the sprayed item is cured (baked), can the paint thickness be measured. A typical range of thickness is between 25 and 200 Microns. A customer may require a certain thickness to their product, and although achievable does takes some skill and years of practice to master. Too much powder can cause the 'orange peel' effect when cured and although this is mainly accepted as part of the process, smoother finishes can be achieved by regulating the flow of powder and lightly blowing off any excess.
Once an item is coated, it is then cured in an oven at around 180 - 200 degrees for approximately 20 - 30 minutes. Heavier metals such as steel posts, gates etc would cure for up to an hour. Sometimes a 'blooming' (haze) effect on the paint happens after curing, this can be wiped off and causes no problem to the paint finish. Powder will only cure once the metal reaches full oven temperature, but will begin to melt at around 150 degrees.
Powder can also be sprayed straight on to hot metal and will melt almost immediately, however an excessive amount of powder will cause drips and runs. It is important to remember less is more when hot coating. Items that generally benefit from hot spraying include: alloy wheels, gates and fencing. This gives a tougher, thicker, smoother finish.
Adding a two-pack primer before spraying, or sanding can add extra life to the product. These things help the paint to adhere to a stronger level, giving you peace of mind.
There are several types of powder for different types of requirements:
- Epoxy Polyester Powders are widely used for internal use only as they do not weather well. They tend to fade and give a chalky appearance.
- Polyester Powders are a good all rounder and are the most commonly used.
These are ideal for external use and stand up to all the elements.
Both Epoxy Polyester and Polyester come in a huge range of colours and can be colour matched to a customers requirements, both can be *over coated, sanded or stripped.
*When over coating its important to remember that with every coat added the thickness is going to increase, and there are only so many coats that can be applied before it will start to chip or crack.
- Nylon Powder is the toughest of all the powders and is used widely for things like handrails and balustrades. It is resistant to scratching and chipping. The only way to remove nylon is by burning it off, it can take sometime and the end result may need some intervention. This would include sand / shot blasting to remove any lasting fragments of paint and revitalise the metal.
At Butler Signs we use bare sheet aluminium and once the panel is folded and welded we lightly sand to give the best possible key for the powder. Sometimes with smaller panels we use an etch primer which eliminates the needs for sanding. We always use Polyester Powder, even for our internal sign panels.