Powder coating

Powder coating

Increasing product durability with powder coatings

If there is one coating that is suitable for almost everything it is powder coating. Liquid paint can be running, sagging and uneven; but powder coatings are applicable as dry, free flowing powder which cures to a smooth and texture free protective (and decorative!) layer. It is no wonder that powder coatings cover more than 15 % of the coating industry in the UK. Powder coating has been available already for more than 60 years!

Because of the enormous possibilities, there are tons of websites with a lot of information to plow through. To make your quest a little easier we have designed this article to answer the most frequently asked questions about both industrial and DIY purposed powder coatings.

The quality of powder coatings improves continuously and they become more and more sustainable as the technology develops. They become suitable for more and more substrates; also heat sensitive such as wood and plastic, they last longer and increase the life time of products, and they are more environmentally friendly than alternative liquid paints.

An inside look into what powder coating is

The basics of what powder coating is remain the same for every industry and substrate.

The paint without a solvent

The amazing thing is that powder coating does not need a solvent to make it liquid for application. The powder is applied directly on the substrate in an electrostatic process.

That is why the main difference and greatest advantage over liquid paint is that powder coating is applicable thinly, evenly and anywhere. Also, being solvent free means, often a more eco-friendly choice than liquid coating.

Fun fact: Powder coating was introduced by Erwin Gemmer, a German scientist, and the patent was issued in September 1955. Back then they were applied by the highly polluting “fluidised bed process”. In 1960 Teodur (now Dupont Powder Coatings, part of Axalta Coating Systems) introduced the environmentally friendly ESD spraying process that is most used today.

But, what is powder coating made of?

Powder coating, as the word implies, is a dry powder based coating. The powder coating powders primarily consist of:

  • Polymer resins 
  • Pigments (in every colour imaginable!)
  • Leveling and drying agents (curatives)
  • Flow modifiers and some other additives

Mixing, melting and cooling these ingredients result in fine dry powder.

Powder coating vs. painting: 3 reasons to go for powder

powder coating vs. painting

The main difference between powder coatings and liquid paints is that the powders do not require solvents in any phase of the application. Therefore, the powders are more eco-friendly than paints which contain solvents that guarantee the flow and evaporate after application.

So, why choose powder?

  1. Uniform, durable coating surface without sagging or running
  2. Close to zero VOC content = environmentally friendly
  3. Fast application and short curing time

Powder coating colours

The good thing about powder coatings is that they are available in every colour of the rainbow. Well, the RAL colour chart.

The one reason why not everyone uses powder coating instead of liquid paint:

One major drawback is that custom colours can be very expensive. Each batch of powder must be ground to order using expensive grinding equipment. Liquid colour will therefore always own their place in the industry. It is easy to mix and match these colours for smaller batches. This makes it more flexible and easy to use.

Let’s get technical: Thermoset & Thermoplastics

As we mentioned above, the powder coatings can be applied in two different ways; dipping and spraying. The two application methods, however, require different properties from the powders. Therefore, powder coating powder can be divided into two types; thermosets, which are suitable for electrostatic spray deposition (ESD) and thermoplastics which are applied by dipping in a fluidised bed. The two types of powders have different properties and applications.

ESD is the application method also suitable for at home applications such as powder coating rims.


All you need to know about how powder coatings work

As we have introduced the coating powder, we’ll now take a closer look into the application process and powder coating methods. The powdercoating process consists of three steps, namely

Chemical cleaning before powder coating

Before (left) & after (right) chemical cleaning

preparation, application and curing. These steps can differ depending on the powder (thermoset/ thermoplastic).

1. The Preperation

For the smooth and even finish, powder coating is famous for, the removal of any oil/grease dirt, metal oxides and other contaminants is essential. There are different methods to accomplish this. The choice of the method is dependent on the size and material of the substrate, and the types of impurities that require removing.

Let’s look at some examples of preparation methods for the most common substrates, and why and when to choose for those methods.

 Method  Chemical cleaning  Method Sandblasting, abrasive blasting & shot blasting
 Substrate  Metal Substrate Wood, Plastic, Glass
 How it works  Multiple stages of degreasing, etching, rinsing and at the end phosphating or chromating the substrate How it works Multiple stages of propelling a high pressure stream of abrasive material forcefully against the substrate
 Advantages Done by a professional, which means the results should be good. Heavily improves adherence to metal Advantages There are several variants of the process; some are highly abrasive, whereas others are milder. Online coating companies that cater to consumers typically offer this extra service at additional costs.
 Disadvantages Chemicals may cause irritation if fumes are inhaled or if they becomes in touch with skin or eyes. Protective means such as gloves and respirator are of high importance. Disadvantages It can present risks for workers health and safety, specifically in portable air blasting or blast room (booth) applications, because of the enormous amount of dust that flies around (lungs, eyes, skin). High standard protective clothing is absolutely necessary.

Tip: If you are powder coating previously painted metal at home, make sure it is brought back to pure metal before applying powder coating on it.


2. The Process & Curing

Let’s start with the ESD…

A special spray gun is the most common tool to apply powdercoatings. The gun, also called corona gun, imparts a positive electric charge to the powder so it adheres to the grounded substrate. It is then cured by heating. The powder melts and forms an even film. After that it’s cooled and forms a hard protective layer. Then the job’s done!

What is powder coating

Man powder coating with protective clothing and corona gun

Electrostatic Powder Spraying Advantages

  • Difficult shapes can be coated;
  • Film thickness between 30-250;
  • Simple and low cost for automation;
  • Changing colour is relatively simple;
  • No pre-heating of components required;
  • Powder residue can be collected and reused

Disadvantage

  • Cost of equipment is higher than a fluidised bed.

A trick of the trade is heating the object beforehand and then spraying powder onto the hot surface. It’s called preheating and results in a more uniform finish. Be careful though; excess powder could cause runs.

Powder coating process electrostatic gun

…And move on to the fluidised bed coating technique.

If you are looking for a different finish you could opt for the electrostatic fluidised bed coating technique. A mouthful, we know!

Let’s explain a bit:

In electrostatic fluidised bed powder coating, heated parts are either dipped directly into a “bed” (container) of fluidised powder or they pass through an electrically charged powder cloud.

Because it has so little waste and has the ability to coat an entire rack of parts by a single dip it is a very efficient method!

It is not suitable for every project though.

  • Thicker layers than with ESD spraying. Because of this, it is very difficult to achieve a thin, consistent coating.
  • Parts that will allow the excess powder to fall off the part are excellent for this process. You should however, avoid objects with areas where air or excess powder can stick.
  • Colour changes can be difficult. You need a different bed for each colour, or you have to change the colour in the bed every time.
  • Smaller details of a part, will most likely be smoothed over because it is thickly applied. Raised lettering, serial numbers and so on will not be visible anymore. Also, if the part has details that are close together, the coating may bridge from one to the other.

Pro tip if you consider purchasing either a Corona gun or electrostatic fluidised bed

If you want to start industrial powder coating in house, and are in doubt of the right investment, realise this:

Fluidised bed coating is a fairly inexpensive system that will give you 100% transfer efficiency. This means virtually no waste. You can achieve the same with electrostatic spray, but it takes a relatively expensive system to get you there.

For this reason the cost of a fluidised bed system is almost always generally lower than the cost of the electrostatic spray equipment needed to achieve the same efficiency.

But remember:

Above we have described different (dis-)advantages of both systems. The right investment always depends on the required finish, object and substrate.

As for home applications, ESD coating can be realised in non-professional environment, but creating a fluidised bed is trickier.


The most common substrate: steel

When working with steel and other metal surfaces the question is; how to best protect the metal from oxidation and weakening keeping in mind the looks of the substrate. The answer naturally is with coating.

But what kind of coating system guarantees the most durability?

Powder coating steel has so far the best results in rust protection and it creates endless possibilities regarding the appearance of steel and other metal surfaces.

Let’s take a look at the powders and their properties:

Epoxy Hybrid Polyurethane Polyester
Hardness Outstanding  Very good  Fair Good
Flexibility Outstanding Outstanding  Outstanding Outstanding
Over bake stability  Fair  Good Outstanding Outstanding
Exterior stability  Poor  Poor Outstanding Outstanding
Corrosion protection Outstanding  Very good  Very good  Very good
Chemical resistance Outstanding  Good  Good  Good
Easy application  Very good  Outstanding  Very good  Very good
Low temperature cure  Outstanding  Very good  Fair  Good
Possibility to powder coat steel

Steel is a term used for ferrous metal alloys, therefore, there are different types of steel such as carbon steel and stainless steel. The steel objects can additionally be pre-treated, which creates more steel types. The most common of these is galvanized steel.

Steel is always electrically conductive and preserves electrostatic charge; therefore, all steel types can be powder coated.

It is however, important to choose the right resin, which provides the wished properties, for the substrate. To give an indication to the compatibility of the resins and substrates, we have put together the following table which explains the steel types and suggests a suitable powder.

Corrosion category Description
C1: Very low  Very little or no pollution (heated buildings such as offices, shops, schools, hotels etc.)
C2: Low  Low levels of pollution (rural areas)
C3: Medium  Urban and industrial areas, moderate sulphur dioxide pollution (coastal areas with low salinity, not under direct influence of salty air or wind)
C4: High  Industrial areas and coastal areas with moderate salinity (sea front areas)
C5 – I: Very high  Industrial areas with high levels of humidity
C5 – M: Very high  Coastal and off-shore areas with high salinity (sea front protection barriers, oil rigs etc.)

Powder coatings alone, does however, not provide the highest possible protection for steel, but it is an essential part of the metal protection system.

Alternative for powder coating steel: Galvanizing

Galvanizing or hot-dipping is an efficient method to make steel and iron corrosion resistant. First you prep the surface by:

  1. Degreasing (chemical cleaning to remove contaminants)
  2. Pickling (dipping in a solution of either hydrochloric or sulfuric acid to remove oxides and mill scale)
  3. Fluxing (the purpose of the flux is to clean the steel of all oxidation developed since the pickling of the steel and to create a protective coating to prevent any oxidation before entering the galvanizing kettle.)

When the steel (or iron) is squeaky clean and completely free of any oxides; the last step is to immerse the object in a bath of molten zinc.

Sounds simple doesn’t it?

That’s because it is! The hot-dip galvanizing process has been around since the year 1742!

Galvanizing process

The steps of a proper galvanizing process

Comparison between galvanizing and powder coating

Galvanizing is sacrificial, which means that the zinc coating slowly corrodes instead of the steel underneath it. Powder coatings on the other hand offer a barrier coating.

Because of the sacrificial protection of galvanizing, scratches in the coating are not that bad. Objects that do not require regular maintenance like electrical towers, are suitable for galvanizing for this reason. While the zinc galvanizing protects the steel, the zinc itself can rapidly corrode if the conditions aren’t right. Galvanizing must “breathe” for proper corrosion resistance. That is why it is not suitable for underwater constructions (off shore or pipelines) Powder coating lasts as long as galvanizing, but once the coating gets damage which exposes the steel, the steel rusts rabidly. When you can’t check for exposure regularly, this is a thing to keep in mind!

The best solution, if you can afford it:

Both paint and powder coatings can be used in conjunction with hot-dip galvanizing, known as a duplex system. The two coatings work in synergy to provide superior corrosion protection, while allowing a specifier to suit any aesthetic preference.

Different substrates; can aluminum, plastic and wood be powder coated?

Among these three substrates aluminum is the easiest to coat. Though some opt for anodising instead of powder coating, it is common to powder coat aluminum. With both glass and wood it’s another story. These materials can’t stand heat very well AND are not electrically conductive. Same goes for plastic. For example powder coating plastic parts is tricky due to the fact that the powder will simply not adhere on these materials.

But the solution is easier than you think!

Pre-heating.  Heat the object in the oven (beware of the melting/burning point) and retract it from the oven. Then powder coat the object while it’s still hot and the powder will melt and stick easily. Then place the object back in the oven for creating an even film.

The trick is:

To not use to much powder. It start’s to melt right away so it might be difficult to see how much you have applied already. There are of course a few other things to consider when you want to powder coat heat sensitive substrates, but it might be a bit much to put in one article. That is why we created a more in dept article about the subject of  how to powdercoat wood and MDF.

Powder coating for internal and external use

powder coating car

For example heat resistant and anti-corrosive powders are used in car manufacturing.

Not all powder coatings are equal. The manufacturer formulates the perfect powder mix for each individual project.

For example, an external coating probably needs to be UV resistant. While an internal coating might need chemical resistant properties, or even non-skid!

  • External powder coating is often based on polyurethane, which has the highest possible resistance to atmospheric conditions.
  • Internal powder coating has more commonly an Epoxy resin basis. They offer flexibility and chemical resistance and are thus perfect for inside tanks and pipes.

Pro tip: Always specify whether the object will be used indoors or outdoors. For example with steel structures that require internal and external powder coatings, be very clear and specific about the conditions and parameters it needs to perform in.

Here’s how to choose the right powdercoating for the job

Choosing the wrong powdercoating could lead to disappointments in the finish. Not only cracking, peeling and/or fading, but you could also miss out on specifically engineered benefits to withstand graffiti, marine environments or chemical environments.  There are even powder formulations which resist damage from light or UV exposure and create a high-gloss, textured or flat matt finish.

No Worries! You won’t miss out:

Express your requirements to your supplier. Your supplier will help you find the right brand and product system to ensure the best results and durability.


What you need to know about the cost to powder coat

Online there is not much information on this subject. And with a reason! Many companies avoid determining the cost to powder coat by a sqm price. It all depends on the finish, the size of the object, the colour you want and many more parameters. Also, due to the fact that the job requires special facilities and powder coating equipment, it is often done by a powder coating specialist.

But don’t worry:

To give you an indication we have taken the liberty to request a quote from different brands. This resulted in a diverse cost overview.

Valspar powder coatings and other brands near you in the UK

One of the leading brands and manufacturers internationally is Valspar powder coatings, or Valspar industries. Their UK branch might be near you! The office and coating platform is located in Liverpool (Goodlass Road) and called Inver UK ltd.

Not near you? Don’t worry:

They are not the only manufacturer in the UK. There are many more good quality suppliers and manufacturers. Most of the suppliers focus on industrial powder coatings but the consumers can also get their hands on a wide range of powder coating products. Many car and paint workshops offer powder coating services, ask around and you might find one closer near you than you thought!

If you are looking to start your own powder coating business The British Coatings Federation is a great help! They offer specified training’s and certificates for the powder coating industry.


Let us help you with your questions regarding powder coating!
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