The Powder Coating Process: A Guide for Manufacturers

Tuesday, March 3 2020 2:21 PM

The powder coating process is commonly used for a number of different applications across multiple industries. It is meant to give more robust protection than traditional liquid paint to things like equipment and vehicles that endure heavy use day in and day out. Today, we are going to take a look at the powder coating process and how you can go about getting the things that are most important coated today!


1. Consultation

The first step you need to take to get your equipment powder coated is to have a consultation. This is what happens when you first contact your powder coating expert and discuss your needs and expectations.

In this initial stage of the process, be sure to outline your project in detail and tell the person you are speaking with exactly what you need and when you need it. 

Sometimes it can be helpful to provide pictures of the equipment you want powdercoated and/or specs on the equipment if available.  

An expert will speak to you about the two different types of powder coating; thermoset and thermoplastic.

  • Thermoset coatings
    • Used for permanent changes to an item 
    • Cannot be re-melted once applied
    • Reinforce the structural integrity of the item 
  • Thermoplastic coatings 
    • Used for items you plan to eventually remold and can be re-melted to allow for updates the item over time 
    • Offers flexible integrity 

You should choose thermotype based on the features of the item and the coat. Thermoset and thermoplastic coatings have different chemical properties and as a result, they can offer different things. 


2. Find the Right Formulation

Once you have discussed the type of coating that would be best for your item, it is time to take a look at powder formulation options. There are several different types of powder coatings and they all offer different benefits depending on your needs.

 

Epoxies

Epoxies are extremely popular as they were the first to be used for this purpose. 

The great thing about epoxies is that they are very durable and offer an environmentally friendly coating that will last for a long time. Epoxy coatings arguably have the best resistance to chemicals and corrosion of all available powders.

Epoxies adhere to metals easily, but the only drawback of this material is that they don’t weather very well so if using outdoors it might not be the best option. 


Polyesters

Polyesters are commonly used as coatings for many different applications. There are two main types: TGIC (triglycidyl isocyanurate) and TGIC-free

One big benefit of the powder is a low cure temperature that makes it ideal for use on smaller components. These offer both great mechanical and impact resistance, as well as chemical resistance. 

TGIC-free polyesters have all the advantages of TGIC polyesters and also give a higher first pass transfer efficiency. It is also important to note that they are more sensitive to excess film thickness and provide less overbake resistance than TGICs.


Super Durable Polyesters

Super Durable Polyesters (SDP) have become popular in recent years because they offer great value for the money and incredible durability. These polyesters are ideal for use in many applications and they hold their color and gloss for an estimated 5-10 years longer than standard polyesters. For corrosion resistance, it is important to use super durable polyesters. 

The only downside here is that SDPs are generally more expensive upfront. 

 

Epoxy-Polyester Hybrids

Epoxies and polyesters can be great alone, but when they are brought together, they get even better. 

Hybrids can be effective and are closer to pure epoxies than polyester. However, the combination of these can bring out the best aspects of each single material. 

The main benefit to mixing these together is negating the weathering effect usually seen by epoxies alone. 

 

Fluoropolymers

Fluoropolymers tend to be used in architectural markets because they have a wonderful resistance to weathering that is not seen in any other material. They are commonly used for windows, walls, and doors. 

 

Urethanes

Urethanes are similar to polyester, however they require a different curing agent to set.

They offer a smooth and sleek finish and they have great durability.  This material is commonly used for things such as agricultural equipment, cars, and other vehicles. 

This material is generally more expensive than the others but if you can budget for it, it is one of the more beautiful powder coated finishes without sacrificing durability. 


3. The Powder Coating Process

Once you have discussed the type of coating as well as the materials you will want your project powder coated with, the powder coating process can begin. 

 

Clean the item 

The first step in the powder coating application process is to clean the item and thoroughly dry it to ensure an even coating. 

When working with a metal object, alkaline cleaning is the most common method used.  

Professionals use alkaline cleaning tanks to do the bulk of the work. 

Cleaning the metal will get rid of any dirt, dust, oils, and residues that may hinder the powder coating process by not allowing the material to adhere to the surface or affect its finish.

When preparing and carrying out alkaline cleaning, there is one factor that must be monitored and maintained: the pH of the bath. 

Alkaline liquid has a pH of above 7; chemicals such as bleach is a common household example of an alkaline liquid. 

There are several different materials that will come off an item and will settle in the bath. These need to be removed throughout the process to avoid accumulation. 

  • Surface oils: Surface oils are removed from the bath using oil skimmers.
  • Particulates: Large particulates can sink and settle at the bottom of the tank. A bag filtration system is used to remove them. 
  • Emulsions and suspended solids: Sometimes emulsions and suspended solids will enter the bath. Ultrafiltration is used to remove these. 

 

Rinse the item 

Once the item is clean, it will be thoroughly rinsed and ready for coating. 

The best practices used for rinsing are:

  • Double counterflow immersion rinse 
  • Reactive rinsing 
  • Spray rinsing
  • Rinse controls 

 

Pre-treatment with Zirconium

A pre-treatment of zirconium is used to chemically convert the metal surface. This facilitates adhesion of the powder coating by providing more sites for the powder coating to bond to. The result is improved corrosion protection and better adhesion. 

Zirconium can be formulated to provide corrosion protection equal to -or better than- phosphates that were traditionally used without the adverse environmental impact. 


4. Drying

The part that is going to be coated needs to be completely dry before any of the powder is applied. 

There are several methods of doing this and the professional you work with likely has a method that works perfectly. 

 

5. Coating

This is part of the process and needs to be carefully managed to provide an efficient and cost-effective result. 

Once the item that needs to be powder coated has been prepared, it is time to apply the powder coating and subsequently dry and cure the item. 

In the powder coating process, dry powder particles are electrostatically charged onto the product or part surface. 

They are applied to the metal part using an electrostatic gun that not only helps the particles adhere to the surface but controls the flow of powder ensuring an even coating

 

5. Curing

Once a coating has been applied to your item, you will need to raise the temperature high enough for it to cure. 

Cure ovens are specifically designed to bake the powder coating and ensure that the coating is durable and completely dry before the item is returned to you. 

The temperature usually increases to about 400°F but can sometimes be a little higher. However, if the right formulation is used curing can be achieved at 325°F and can reduce the amount of energy used. 

Learn More About Industrial Powder Coating

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