Powder Coatings

This mainly deals with the preparation of the part or component.  And just as any other paint application, preparation is all necessary so as to be able to achieve the best possible finish. During this phase, it is essentially removing all the metal oxides, lubricants, and oils. This is usually done by the use of some mechanical and chemical processes depending on the finish required, its size, and the material.

The multiple stage chemical pre-treatment entails using the chromates and phosphates by spraying or submersion. However, from the environmental view, the most ideal component during the preparation process is the phosphate as the chromates could be environment toxic. Another method that can be used in the preparation is the shot blasting and sandblasting. This is where the blasting abrasives are used in giving the surface texture and the preparation of glass, plastic, and wood. Silicon carbide is the most appropriate when it comes to metal grinding.  The plastic media blasting however uses the plastic abrasives that are usually that sensitive to the substrates like aluminum.

The most common method used in the powder coating application is electrostatic spraying through a spray gun. In this case, the objects get grounded and the gun imparts positive electric charges onto the powder. This is then accelerated and sprayed towards the components using the power of the electrostatic charges. The component is then later heated and the powder melts into a uniform film that cools forming the hard coatings.  However, sometimes the metal is heated first and then the powder sprayed onto the hot substrate.   These pre-heating techniques can aid in the achievement of more uniform finishes. However, this can have other problems such as runs due to excessive powder. More so, the powder can be applied using the precisely adapted electrostatic discs.

Another method is the Electrostatic Fluidised Bed Coating. This is whereby the electrostatic charging will occur in the bed so that the powder becomes charged while the fluidizing air is lifting it up. The powder particles that are charged then form a cloud of powder above the fluid beds.  When thus a grounded part passes through the charged cloud, these particles get attracted to these surfaces. Typically, these parts are not always preheated. Lastly, we have the Electrostatic Magnetic Brush (EMB) coating. This coating is mainly used for the flat materials and regularly applies the powder coating using the roller technique.

When the thermosets powders get exposed to the high temperatures, they start melting, flowing out, and reacting forming higher molecular weight polymers.  This curing process known as the cross-linking will thus need a certain temperature degree for a certain duration for it to get full cure thus establishing the full film properties that the materials were designed.