By Dominic Scholes

Anthony Mount

Powder coating works by electrostatically charging the item to be coated and then charging the powder to do the coating with the opposite polarity. The powder is then ‘sprayed’ at a low pressure at the  object to be coated. I now use a normal industrial type air compressor but in the past have used an airbrush compressor, so they don't consume much air.

The powder is attracted to the part to be finished as it is electrostatically charged and this is how the coating is applied. At this stage the powder can be brushed off, and to bond it to the part it needs to be baked at 185degC where the powder will fuse into a solid coating.

The Hotcoat powder coating kit

Photo: Dominic Scholes

A few years ago I bought a powder coating gun so I could do powder coating at home. At the time I bought an Eastwood's Hotcoat setup (usual disclaimer) that is marketed. I got it for finishing small metal items as I thought it would be easier than cleaning spray guns and cheaper than aerosols for normal part finishing. This is the powder coating gun I use, and I'm thinking you could make one at home and use a car ignition coil (and simple electronics) to create the high voltage to do the electrostatic charging) the gun is simple machining of plastics. The powders are available in small quantities, so you don't need buy industrial quantities.

As this is only occasionally used, I decided to keep it all in a plastic storage tub to keep everything together when not in use.

The plastic storage tub

Photo: Dominic Scholes

This tub has been modified to be used as a small powder coating booth. It is used on its side and has a brass rod with a hook on the end that goes through the side and is clamped between a couple of pieces of wood which allows me to rotate the part to be coated and also adjust its height.

The brass rod is connected to the electronic module by a crocodile clip.

As with most metal finishing, preparation is the key, and powder coating is no exception and in some  places has a bad reputation for flaking, but as it is applied to a smooth surface you can expect that. These steel brackets have been lightly grit blasted to improve the adhesion.

They were then washed and baked in an oven to dry them. If the object has been degreased, I'd normally bake the part in an oven at 200degC for 30 minutes to boil off any solvents trapped in surface imperfections. If this isn't done until the powder coating is baked then it can result in blisters or holes in the coating surface.

The tub in powder-coating mode

Photo: Dominic Scholes

Items ready for coating

Photo: Dominic Scholes

If you want to mask something so an area is not coated, you can't use normal masking tape as it will burn off due to the baking temperature. The normal process would be to fit silicone rubber bungs to holes or use polyimide/Kapton tape for other areas as this is designed for high temperature use. (And just wondering now if it can be used for masking when soft soldering?).

When it comes to applying the powder, it is ‘sprayed’ at the area to be coated, but the parts should only be electrostatically charged when the powder is being applied as the charge is

The part with its powder coating

Photo: Dominic Scholes

high voltage and you can get 25mm long sparks if the gun goes too close to the object being coated.

One issue with powder coating is that sometimes it is difficult for the powder to coat enclosed or sharp corners and this is known as the "Faraday Cage effect" but there are ways to get round that.

One advantage of powder coating is that its very difficult to have too thick a layer and get runs in the finish (unlike spray painting). Another advantage of powder coating is that if you're not happy with the application of powder, you can brush it off and start again (unlike spray painting).

The parts ready for baking

Photo: Dominic Scholes

A thin metal hook is used to hold the part to be coated as you can't touch the item to be coated until the powder has been baked on, as if you do, it will just remove the coating. I apply the powder outdoors  as the powder is a very fine dust and gets everywhere.

The final part is to bake the powder coating and fuse it into a surface finish, and I do this in a domestic oven at 185degC (I don't cook food in it), but air fryers and worktop mini ovens (not microwave ovens) can also be used (fan assisted ovens might disturb the coating - Ed)).

Normally, the powder coating is baked at 185degC for 20 minutes to fuse it together, but you need to allow time for the heat to soak into the part so it can get up to temperature. For small brackets like this I'll bake them for 30 minutes, but for something larger (like a brake caliper)

I'd bake them for 45 minutes.

Collecting the excess powder

Photo: Dominic Scholes

Once you have finished the coating, the excess powder can be brushed up and re-used, which makes it a much more economical process, and it helps that I have the plastic storage tub to use as a spray booth.

One advantage of powder coating is that as soon as the parts are cool enough to hold after baking, they can be used. Quicker than waiting two or three days for spray paint to harden!

So there you are, a brief introduction  to powder coating at home. It is another tool to have in your box and is an alternative to the usual methods of metal finishing. It can produce good results economically after the initial outlay on equipment has been spent.

The finished parts, all nice and shiny

Photo: Dominic Scholes

This article first appeared in the Bradford MES Bulletin